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 08e6316..350c3f6 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
@@ -7,6 +7,7 @@
 import java.util.*;
 import java.util.LinkedList;
 
+// TODO: visualize cfg
 public class CFG<I extends IRNode> implements Iterable<BasicBlock<I>> {
     public final List<BasicBlock<I>> nodes;