diff --git a/ep16/src/main/java/org/teachfx/antlr4/ep16/Compiler.java b/ep16/src/main/java/org/teachfx/antlr4/ep16/Compiler.java
index 7ca9d1d..2dd7e11 100644
--- a/ep16/src/main/java/org/teachfx/antlr4/ep16/Compiler.java
+++ b/ep16/src/main/java/org/teachfx/antlr4/ep16/Compiler.java
@@ -11,7 +11,9 @@
 import org.teachfx.antlr4.ep16.visitor.LocalDefine;
 import org.teachfx.antlr4.ep16.visitor.LocalResolver;
 
-import java.io.*;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
 
 public class Compiler {
 
diff --git a/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolLexer.java b/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolLexer.java
index 26ee17d..ee76e77 100644
--- a/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolLexer.java
+++ b/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep16.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolLexer extends Lexer {
diff --git a/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolParser.java b/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolParser.java
index 39caa2d..1035df6 100644
--- a/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolParser.java
+++ b/ep16/src/main/java/org/teachfx/antlr4/ep16/parser/CymbolParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep16.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolParser extends Parser {
diff --git a/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolLexer.java b/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolLexer.java
index eb1a7a1..51e507c 100644
--- a/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolLexer.java
+++ b/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep17.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolLexer extends Lexer {
diff --git a/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolParser.java b/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolParser.java
index 387aada..a77ae6c 100644
--- a/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolParser.java
+++ b/ep17/src/main/java/org/teachfx/antlr4/ep17/parser/CymbolParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep17.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolParser extends Parser {
diff --git a/ep17/src/main/java/org/teachfx/antlr4/ep17/visitor/CallGraphVisitor.java b/ep17/src/main/java/org/teachfx/antlr4/ep17/visitor/CallGraphVisitor.java
index 48f5b7a..b5705a8 100644
--- a/ep17/src/main/java/org/teachfx/antlr4/ep17/visitor/CallGraphVisitor.java
+++ b/ep17/src/main/java/org/teachfx/antlr4/ep17/visitor/CallGraphVisitor.java
@@ -2,7 +2,8 @@
 
 import org.teachfx.antlr4.ep17.misc.Graph;
 import org.teachfx.antlr4.ep17.parser.CymbolBaseVisitor;
-import org.teachfx.antlr4.ep17.parser.CymbolParser.*;
+import org.teachfx.antlr4.ep17.parser.CymbolParser.ExprFuncCallContext;
+import org.teachfx.antlr4.ep17.parser.CymbolParser.FunctionDeclContext;
 public class CallGraphVisitor extends CymbolBaseVisitor<Object> {
     public Graph callGraph;
     private String currentFunctionName = null;
diff --git a/ep18/src/main/java/org/teachfx/antlr4/ep18/VMInterpreter.java b/ep18/src/main/java/org/teachfx/antlr4/ep18/VMInterpreter.java
index 49c1faf..c2080d4 100644
--- a/ep18/src/main/java/org/teachfx/antlr4/ep18/VMInterpreter.java
+++ b/ep18/src/main/java/org/teachfx/antlr4/ep18/VMInterpreter.java
@@ -4,9 +4,9 @@
 import org.antlr.v4.runtime.CommonTokenStream;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.runtime.tree.ParseTreeWalker;
-import org.teachfx.antlr4.ep18.stackvm.*;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerLexer;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerParser;
+import org.teachfx.antlr4.ep18.stackvm.*;
 
 import java.io.FileInputStream;
 import java.io.InputStream;
diff --git a/ep18/src/main/java/org/teachfx/antlr4/ep18/VMRunner.java b/ep18/src/main/java/org/teachfx/antlr4/ep18/VMRunner.java
index b4d3869..ef373d6 100644
--- a/ep18/src/main/java/org/teachfx/antlr4/ep18/VMRunner.java
+++ b/ep18/src/main/java/org/teachfx/antlr4/ep18/VMRunner.java
@@ -5,10 +5,10 @@
 import org.antlr.v4.runtime.CommonTokenStream;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.runtime.tree.ParseTreeWalker;
-import org.teachfx.antlr4.ep18.stackvm.ByteCodeAssembler;
-import org.teachfx.antlr4.ep18.stackvm.BytecodeDefinition;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerLexer;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerParser;
+import org.teachfx.antlr4.ep18.stackvm.ByteCodeAssembler;
+import org.teachfx.antlr4.ep18.stackvm.BytecodeDefinition;
 
 import java.io.FileInputStream;
 import java.io.InputStream;
diff --git a/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerLexer.java b/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerLexer.java
index fbe5856..3602a4e 100644
--- a/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerLexer.java
+++ b/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep18.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class VMAssemblerLexer extends Lexer {
diff --git a/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerParser.java b/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerParser.java
index 050cba9..9cce11b 100644
--- a/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerParser.java
+++ b/ep18/src/main/java/org/teachfx/antlr4/ep18/parser/VMAssemblerParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep18.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class VMAssemblerParser extends Parser {
diff --git a/ep18/src/main/java/org/teachfx/antlr4/ep18/stackvm/ByteCodeAssembler.java b/ep18/src/main/java/org/teachfx/antlr4/ep18/stackvm/ByteCodeAssembler.java
index 9fb4523..da7571c 100644
--- a/ep18/src/main/java/org/teachfx/antlr4/ep18/stackvm/ByteCodeAssembler.java
+++ b/ep18/src/main/java/org/teachfx/antlr4/ep18/stackvm/ByteCodeAssembler.java
@@ -3,8 +3,10 @@
 import org.antlr.v4.runtime.Token;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerBaseListener;
 import org.teachfx.antlr4.ep18.parser.VMAssemblerParser;
-import org.teachfx.antlr4.ep18.parser.*;
-import org.teachfx.antlr4.ep18.parser.VMAssemblerParser.*;
+import org.teachfx.antlr4.ep18.parser.VMAssemblerParser.FunctionDeclarationContext;
+import org.teachfx.antlr4.ep18.parser.VMAssemblerParser.GlobalsContext;
+import org.teachfx.antlr4.ep18.parser.VMAssemblerParser.InstrContext;
+import org.teachfx.antlr4.ep18.parser.VMAssemblerParser.LabelContext;
 
 import java.util.ArrayList;
 import java.util.HashMap;
diff --git a/ep19/src/main/java/org/teachfx/antlr4/ep19/Compiler.java b/ep19/src/main/java/org/teachfx/antlr4/ep19/Compiler.java
index be98c41..2104898 100644
--- a/ep19/src/main/java/org/teachfx/antlr4/ep19/Compiler.java
+++ b/ep19/src/main/java/org/teachfx/antlr4/ep19/Compiler.java
@@ -11,7 +11,10 @@
 import org.teachfx.antlr4.ep19.pass.LocalDefine;
 import org.teachfx.antlr4.ep19.pass.LocalResolver;
 
-import java.io.*;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
 
 public class Compiler {
 
diff --git a/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolLexer.java b/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolLexer.java
index c3f8960..5892c70 100644
--- a/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolLexer.java
+++ b/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep19.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolLexer extends Lexer {
diff --git a/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolParser.java b/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolParser.java
index f2eca1d..e352c51 100644
--- a/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolParser.java
+++ b/ep19/src/main/java/org/teachfx/antlr4/ep19/parser/CymbolParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep19.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolParser extends Parser {
diff --git a/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/CymbolASTVisitor.java b/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/CymbolASTVisitor.java
index 85f1616..b06b7d3 100644
--- a/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/CymbolASTVisitor.java
+++ b/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/CymbolASTVisitor.java
@@ -2,7 +2,10 @@
 
 import org.teachfx.antlr4.ep19.misc.Util;
 import org.teachfx.antlr4.ep19.parser.CymbolBaseVisitor;
-import org.teachfx.antlr4.ep19.parser.CymbolParser.*;
+import org.teachfx.antlr4.ep19.parser.CymbolParser.BlockContext;
+import org.teachfx.antlr4.ep19.parser.CymbolParser.ExprFuncCallContext;
+import org.teachfx.antlr4.ep19.parser.CymbolParser.FunctionDeclContext;
+import org.teachfx.antlr4.ep19.parser.CymbolParser.StructDeclContext;
 
 public abstract class CymbolASTVisitor<T> extends CymbolBaseVisitor<T> {
     public String tab = "";
diff --git a/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/LocalDefine.java b/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/LocalDefine.java
index 9ea7ab4..372b284 100644
--- a/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/LocalDefine.java
+++ b/ep19/src/main/java/org/teachfx/antlr4/ep19/pass/LocalDefine.java
@@ -3,11 +3,15 @@
 import org.antlr.v4.runtime.ParserRuleContext;
 import org.antlr.v4.runtime.tree.ParseTreeProperty;
 import org.teachfx.antlr4.ep19.misc.Util;
-import org.teachfx.antlr4.ep19.symtab.TypeTable;
-import org.teachfx.antlr4.ep19.symtab.scope.*;
-import org.teachfx.antlr4.ep19.symtab.symbol.*;
-import org.teachfx.antlr4.ep19.parser.CymbolBaseVisitor;
 import org.teachfx.antlr4.ep19.parser.CymbolParser.*;
+import org.teachfx.antlr4.ep19.symtab.TypeTable;
+import org.teachfx.antlr4.ep19.symtab.scope.BaseScope;
+import org.teachfx.antlr4.ep19.symtab.scope.GlobalScope;
+import org.teachfx.antlr4.ep19.symtab.scope.LocalScope;
+import org.teachfx.antlr4.ep19.symtab.scope.Scope;
+import org.teachfx.antlr4.ep19.symtab.symbol.MethodSymbol;
+import org.teachfx.antlr4.ep19.symtab.symbol.StructSymbol;
+import org.teachfx.antlr4.ep19.symtab.symbol.VariableSymbol;
 
 /**
  *
diff --git a/ep20/README.md b/ep20/README.md
index 168c6a3..722cdc4 100644
--- a/ep20/README.md
+++ b/ep20/README.md
@@ -35,6 +35,61 @@ graph LR
 ### CFG
 
 ```mermaid
-graph TD;
-    L0["iconst 0;istore 0;;iconst 7;igt"]
-```
\ No newline at end of file
+graph LR;
+    .def dec1: args=1 ,locals=1[t0 = @0;
+t1 =  1 ;
+t0 SUB t1;
+jmp L1;
+]
+L1[ret;
+]
+.def main: args=0 ,locals=1[t0 =  10 ;
+@0 = t0;
+jmp L4;
+]
+L4[t0 = @0;
+t1 =  0 ;
+t0 GT t1;
+jmpIf t0,L5,L6;
+]
+L5[t0 = @0;
+t1 =  5 ;
+t0 GT t1;
+jmpIf t0,L7,L8;
+]
+L7[t0 = @0;
+call print(args:1);
+t0 = @0;
+t1 =  7 ;
+t0 EQ t1;
+jmpIf t0,L9,L10;
+]
+L9[t0 =  7 ;
+jmp L3;
+]
+L10[]
+L8[t0 =  "break" ;
+call print(args:1);
+t0 = @0;
+call dec1(args:1);
+@0 = t0;
+jmp L4;
+]
+L6[t0 =  0 ;
+jmp L3;
+]
+L3[halt;
+]
+L0 --> L1
+L2 --> L4
+L4 --> L5
+L5 --> L7
+L7 --> L9
+L9 --> L10
+L10 --> L8
+L8 --> L6
+L6 --> L3
+
+
+```
+
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
index bfb8d43..d590d27 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
@@ -12,7 +12,6 @@
 import org.teachfx.antlr4.ep20.parser.CymbolLexer;
 import org.teachfx.antlr4.ep20.parser.CymbolParser;
 import org.teachfx.antlr4.ep20.pass.ast.CymbolASTBuilder;
-
 import org.teachfx.antlr4.ep20.pass.codegen.CymbolAssembler;
 import org.teachfx.antlr4.ep20.pass.ir.CymbolIRBuilder;
 import org.teachfx.antlr4.ep20.pass.symtab.LocalDefine;
@@ -51,7 +50,7 @@ public static void main(String[] args) throws IOException {
         astRoot.accept(irBuilder);
 
         var cfg = irBuilder.getCFG();
-        logger.info("CFG:\n" + cfg);
+        logger.info("CFG:\n" + cfg.toString());
 
         var assembler = new CymbolAssembler();
         irBuilder.prog.accept(assembler);
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/val/ConstVal.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/val/ConstVal.java
index 5d7b3c4..d2fcd0e 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/val/ConstVal.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/val/ConstVal.java
@@ -30,7 +30,7 @@ public void setVal(T val) {
     @Override
     public String toString() {
         if(val instanceof String) {
-            return " %s ".formatted(val);
+            return " '%s' ".formatted(val);
         } else if (val instanceof Integer) {
             return " %d ".formatted(val);
         } else if (val instanceof Boolean) {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/CJMP.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/CJMP.java
index 85fe7ed..ec27d1c 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/CJMP.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/CJMP.java
@@ -1,8 +1,8 @@
 package org.teachfx.antlr4.ep20.ir.stmt;
 
-import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 import org.teachfx.antlr4.ep20.ir.IRVisitor;
 import org.teachfx.antlr4.ep20.ir.expr.VarSlot;
+import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 
 public class CJMP extends Stmt {
     public VarSlot cond;
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/JMP.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/JMP.java
index 839b015..77b8853 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/JMP.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/JMP.java
@@ -1,7 +1,7 @@
 package org.teachfx.antlr4.ep20.ir.stmt;
 
-import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 import org.teachfx.antlr4.ep20.ir.IRVisitor;
+import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 
 public class JMP extends Stmt
 {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolLexer.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolLexer.java
index 790fb64..093d6fd 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolLexer.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep20.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolLexer extends Lexer {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolParser.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolParser.java
index fd41f27..9c0f76e 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolParser.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/parser/CymbolParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep20.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolParser extends Parser {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ast/CymbolASTBuilder.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ast/CymbolASTBuilder.java
index 9ddf0ad..d3b4044 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ast/CymbolASTBuilder.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ast/CymbolASTBuilder.java
@@ -215,7 +215,9 @@ public ASTNode visitPrimaryFLOAT(CymbolParser.PrimaryFLOATContext ctx) {
 
     @Override
     public ASTNode visitPrimarySTRING(CymbolParser.PrimarySTRINGContext ctx) {
-        return new StringExprNode(ctx.getText(),ctx);
+        var size = ctx.getText().length();
+
+        return new StringExprNode(ctx.getText().substring(1, size - 1),ctx);
     }
 
     @Override
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
index 8502e2d..2a09370 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
@@ -2,7 +2,6 @@
 
 import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
-
 import org.teachfx.antlr4.ep20.ir.IRNode;
 import org.teachfx.antlr4.ep20.ir.expr.Operand;
 import org.teachfx.antlr4.ep20.ir.stmt.Label;
@@ -73,6 +72,10 @@ public Optional<Label> getLabel() {
         return label;
     }
 
+    public String getOrdLabel() {
+        return "L%d".formatted(id);
+    }
+
     // Generate isEmpty
     public boolean isEmpty() {
         return codes.isEmpty();
@@ -84,6 +87,10 @@ public List<Loc<I>> allSeq() {
         return codes.subList(0, codes.size() - 1);
     }
 
+    public List<Loc<I>> dropLabelSeq() {
+        return codes.subList(1, codes.size());
+    }
+
     public I getLastInstr() {
         return codes.get(codes.size() - 1).instr;
     }
@@ -96,4 +103,5 @@ public I getLastInstr() {
     public Set<Operand> liveIn;
 
     public Set<Operand> liveOut;
+
 }
\ No newline at end of file
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
index 350c3f6..7f4d67d 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
@@ -1,19 +1,25 @@
 package org.teachfx.antlr4.ep20.pass.cfg;
 
 import org.apache.commons.lang3.tuple.Pair;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.jetbrains.annotations.NotNull;
 import org.teachfx.antlr4.ep20.ir.IRNode;
 
 import java.util.*;
-import java.util.LinkedList;
+import java.util.concurrent.atomic.AtomicInteger;
 
 // TODO: visualize cfg
+/*
+    One graph bind to a function.
+ */
 public class CFG<I extends IRNode> implements Iterable<BasicBlock<I>> {
+    private final static Logger logger = LogManager.getLogger(CFG.class);
     public final List<BasicBlock<I>> nodes;
 
     public final List<Pair<Integer,Integer>> edges;
 
-    private List<Pair<Set<Integer>, Set<Integer>>> links;
+    private final List<Pair<Set<Integer>, Set<Integer>>> links;
 
     public CFG(List<BasicBlock<I>> nodes, List<Pair<Integer, Integer>> edges) {
         // Generate init
@@ -30,7 +36,6 @@ public CFG(List<BasicBlock<I>> nodes, List<Pair<Integer, Integer>> edges) {
              var v = edge.getRight();
              links.get(u).getRight().add(v);
              links.get(v).getLeft().add(u);
-
         }
     }
 
@@ -63,8 +68,24 @@ public Iterator<BasicBlock<I>> iterator() {
 
     @Override
     public String toString() {
-        var graphRenderBuffer = new StringBuffer();
+        var graphRenderBuffer = new StringBuilder("graph LR\n");
+        AtomicInteger i = new AtomicInteger();
+
+        for(var node : nodes){
+
+            graphRenderBuffer.append("subgraph ").append(node.getOrdLabel()).append("\n");
+            node.dropLabelSeq().stream().map(x -> x.instr.toString()).map(x ->  "Q"+ (i.getAndIncrement()) + "[\"" + x + ";\"]\n").forEach(graphRenderBuffer::append);
+            graphRenderBuffer.append("end").append("\n");
+
+        }
+
+        for (var edge : edges){
+
+            graphRenderBuffer.append("L").append(edge.getLeft()).append(" --> ").append("L").append(edge.getRight()).append("\n");
+        }
 
         return graphRenderBuffer.toString();
     }
+
+
 }
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
index 36d134b..8fdc151 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
@@ -5,7 +5,6 @@
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Map;
 
 public class CFGBuilder {
     private CFG<IRNode> cfg;
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
index 6d18905..60d9e5f 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
@@ -137,7 +137,7 @@ public <T> Void visit(ConstVal<T> tConstVal) {
         if (tConstVal.getVal() instanceof Integer integer) {
             emit("iconst %d".formatted(integer));
         } else if (tConstVal.getVal() instanceof String str) {
-            emit("sconst %s".formatted(str));
+            emit("sconst \"%s\"".formatted(str));
         } else if (tConstVal.getVal() instanceof Boolean bool) {
             emit("bconst %d".formatted(bool?1:0));
         }
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
index f41b6bb..808df74 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
@@ -10,13 +10,10 @@
 import org.teachfx.antlr4.ep20.ast.expr.*;
 import org.teachfx.antlr4.ep20.ast.stmt.*;
 import org.teachfx.antlr4.ep20.ast.type.TypeNode;
-import org.teachfx.antlr4.ep20.ir.expr.Operand;
-import org.teachfx.antlr4.ep20.pass.cfg.CFG;
-import org.teachfx.antlr4.ep20.pass.cfg.CFGBuilder;
-import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 import org.teachfx.antlr4.ep20.ir.IRNode;
 import org.teachfx.antlr4.ep20.ir.Prog;
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
+import org.teachfx.antlr4.ep20.ir.expr.Operand;
 import org.teachfx.antlr4.ep20.ir.expr.VarSlot;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
 import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
@@ -24,10 +21,12 @@
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
 import org.teachfx.antlr4.ep20.ir.stmt.*;
+import org.teachfx.antlr4.ep20.pass.cfg.CFG;
+import org.teachfx.antlr4.ep20.pass.cfg.CFGBuilder;
+import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 import org.teachfx.antlr4.ep20.symtab.symbol.MethodSymbol;
 import org.teachfx.antlr4.ep20.symtab.symbol.VariableSymbol;
 
-import java.util.Objects;
 import java.util.Optional;
 import java.util.Stack;
 
diff --git a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
index 28f78f2..01efecc 100644
--- a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
+++ b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
@@ -3,7 +3,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class CymbolAssemblerTest {
diff --git a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/sematic/TypeCheckerTest.java b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/sematic/TypeCheckerTest.java
index 41e367d..a3c2460 100644
--- a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/sematic/TypeCheckerTest.java
+++ b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/sematic/TypeCheckerTest.java
@@ -3,8 +3,6 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 
-import static org.junit.jupiter.api.Assertions.*;
-
 class TypeCheckerTest {
 
     @BeforeEach
diff --git a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/symtab/LocalDefineTest.java b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/symtab/LocalDefineTest.java
index 3722de3..3d4faf8 100644
--- a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/symtab/LocalDefineTest.java
+++ b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/symtab/LocalDefineTest.java
@@ -4,8 +4,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
-
 class LocalDefineTest {
     @BeforeEach
     void setUp() {
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/driver/Phase.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/driver/Phase.java
index 83f8a85..4bad0f5 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/driver/Phase.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/driver/Phase.java
@@ -1,5 +1,4 @@
 package org.teachfx.antlr4.ep21.driver;
-import org.teachfx.antlr4.ep21.error.CymbalError;
 
 import java.util.Optional;
 
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/ir/IRVisitor.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/ir/IRVisitor.java
index f38d84c..1a76244 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/ir/IRVisitor.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/ir/IRVisitor.java
@@ -1,7 +1,10 @@
 package org.teachfx.antlr4.ep21.ir;
 
 import org.teachfx.antlr4.ep21.ir.def.Func;
-import org.teachfx.antlr4.ep21.ir.expr.*;
+import org.teachfx.antlr4.ep21.ir.expr.ArrayAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.CallFunc;
+import org.teachfx.antlr4.ep21.ir.expr.ClassAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.Temp;
 import org.teachfx.antlr4.ep21.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep21.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep21.ir.expr.values.BoolVal;
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolLexer.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolLexer.java
index d425e5c..cf74b5a 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolLexer.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolLexer.java
@@ -2,14 +2,12 @@
 
 package org.teachfx.antlr4.ep21.parser;
 
-import org.antlr.v4.runtime.Lexer;
-import org.antlr.v4.runtime.CharStream;
-import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.TokenStream;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
 import org.antlr.v4.runtime.dfa.DFA;
-import org.antlr.v4.runtime.misc.*;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolLexer extends Lexer {
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolParser.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolParser.java
index bb9117c..b74a094 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolParser.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/parser/CymbolParser.java
@@ -2,14 +2,17 @@
 
 package org.teachfx.antlr4.ep21.parser;
 
-import org.antlr.v4.runtime.atn.*;
-import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.misc.*;
-import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.atn.ATN;
+import org.antlr.v4.runtime.atn.ATNDeserializer;
+import org.antlr.v4.runtime.atn.ParserATNSimulator;
+import org.antlr.v4.runtime.atn.PredictionContextCache;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+import org.antlr.v4.runtime.tree.ParseTreeVisitor;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
 import java.util.List;
-import java.util.Iterator;
-import java.util.ArrayList;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue"})
 public class CymbolParser extends Parser {
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/BasicBlock.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/BasicBlock.java
index 9c69de5..5bf3d47 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/BasicBlock.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/BasicBlock.java
@@ -1,7 +1,6 @@
 package org.teachfx.antlr4.ep21.pass.cfg;
 
 import org.teachfx.antlr4.ep21.ir.IRNode;
-import org.teachfx.antlr4.ep21.ir.stmt.Label;
 
 import java.util.List;
 
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/ControlFlowAnalysis.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/ControlFlowAnalysis.java
index 648da7c..f208965 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/ControlFlowAnalysis.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/cfg/ControlFlowAnalysis.java
@@ -3,7 +3,10 @@
 import org.teachfx.antlr4.ep21.ir.IRVisitor;
 import org.teachfx.antlr4.ep21.ir.Prog;
 import org.teachfx.antlr4.ep21.ir.def.Func;
-import org.teachfx.antlr4.ep21.ir.expr.*;
+import org.teachfx.antlr4.ep21.ir.expr.ArrayAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.CallFunc;
+import org.teachfx.antlr4.ep21.ir.expr.ClassAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.Temp;
 import org.teachfx.antlr4.ep21.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep21.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep21.ir.expr.values.BoolVal;
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/codegen/CymbolAssembler.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/codegen/CymbolAssembler.java
index 7f2323b..9a51b9d 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/codegen/CymbolAssembler.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/codegen/CymbolAssembler.java
@@ -3,7 +3,10 @@
 import org.teachfx.antlr4.ep21.ir.IRVisitor;
 import org.teachfx.antlr4.ep21.ir.Prog;
 import org.teachfx.antlr4.ep21.ir.def.Func;
-import org.teachfx.antlr4.ep21.ir.expr.*;
+import org.teachfx.antlr4.ep21.ir.expr.ArrayAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.CallFunc;
+import org.teachfx.antlr4.ep21.ir.expr.ClassAccessExpr;
+import org.teachfx.antlr4.ep21.ir.expr.Temp;
 import org.teachfx.antlr4.ep21.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep21.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep21.ir.expr.values.BoolVal;
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/ir/CymbolIRBuilder.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/ir/CymbolIRBuilder.java
index b420f30..3d05027 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/ir/CymbolIRBuilder.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/pass/ir/CymbolIRBuilder.java
@@ -2,7 +2,6 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-
 import org.teachfx.antlr4.ep21.ast.ASTVisitor;
 import org.teachfx.antlr4.ep21.ast.CompileUnit;
 import org.teachfx.antlr4.ep21.ast.decl.FuncDeclNode;
@@ -12,7 +11,8 @@
 import org.teachfx.antlr4.ep21.ast.type.TypeNode;
 import org.teachfx.antlr4.ep21.ir.Prog;
 import org.teachfx.antlr4.ep21.ir.def.Func;
-import org.teachfx.antlr4.ep21.ir.expr.*;
+import org.teachfx.antlr4.ep21.ir.expr.CallFunc;
+import org.teachfx.antlr4.ep21.ir.expr.Expr;
 import org.teachfx.antlr4.ep21.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep21.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep21.ir.expr.values.BoolVal;
diff --git a/ep21/src/main/java/org/teachfx/antlr4/ep21/symtab/scope/LocalScope.java b/ep21/src/main/java/org/teachfx/antlr4/ep21/symtab/scope/LocalScope.java
index 29fa3a8..8fe6c48 100644
--- a/ep21/src/main/java/org/teachfx/antlr4/ep21/symtab/scope/LocalScope.java
+++ b/ep21/src/main/java/org/teachfx/antlr4/ep21/symtab/scope/LocalScope.java
@@ -2,7 +2,6 @@
 
 import org.teachfx.antlr4.ep21.ast.stmt.ScopeType;
 import org.teachfx.antlr4.ep21.symtab.symbol.Symbol;
-import org.teachfx.antlr4.ep21.symtab.type.BuiltInTypeSymbol;
 
 public class LocalScope extends BaseScope {
     // Generate seq code for local variables follow GlobalScope
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/BoolExprNodeTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/BoolExprNodeTest.java
index 9895308..531ae0b 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/BoolExprNodeTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/BoolExprNodeTest.java
@@ -2,7 +2,7 @@
 
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class BoolExprNodeTest {
 
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/FloatExprNodeTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/FloatExprNodeTest.java
index 09db8b0..a749797 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/FloatExprNodeTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/FloatExprNodeTest.java
@@ -2,7 +2,7 @@
 
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class FloatExprNodeTest {
     @Test
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/StringExprNodeTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/StringExprNodeTest.java
index 7a91c2b..4615307 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/StringExprNodeTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/StringExprNodeTest.java
@@ -2,7 +2,7 @@
 
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class StringExprNodeTest {
 
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/UnaryExprNodeTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/UnaryExprNodeTest.java
index 4eaba32..d2b241e 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/UnaryExprNodeTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/ast/expr/UnaryExprNodeTest.java
@@ -1,9 +1,10 @@
 package org.teachfx.antlr4.ep21.ast.expr;
 
 import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.*;
 import org.teachfx.antlr4.ep21.symtab.type.OperatorType;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 class UnaryExprNodeTest {
     @Test
     public void testNegInt() {
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/sematic/TypeCheckerTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/sematic/TypeCheckerTest.java
index a070772..44ff026 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/sematic/TypeCheckerTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/sematic/TypeCheckerTest.java
@@ -3,8 +3,6 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 
-import static org.junit.jupiter.api.Assertions.*;
-
 class TypeCheckerTest {
 
     @BeforeEach
diff --git a/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/symtab/LocalDefineTest.java b/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/symtab/LocalDefineTest.java
index ed57b19..d8bc326 100644
--- a/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/symtab/LocalDefineTest.java
+++ b/ep21/src/test/java/org/teachfx/antlr4/ep21/pass/symtab/LocalDefineTest.java
@@ -4,8 +4,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
-
 class LocalDefineTest {
     @BeforeEach
     void setUp() {