diff --git a/AlgebraicDataflowArchitectureModel/src/code/ast/Expression.java b/AlgebraicDataflowArchitectureModel/src/code/ast/Expression.java
index d492947..efa14f3 100644
--- a/AlgebraicDataflowArchitectureModel/src/code/ast/Expression.java
+++ b/AlgebraicDataflowArchitectureModel/src/code/ast/Expression.java
@@ -6,4 +6,14 @@
  * @author s-yamagiwa
  */
 public abstract class Expression extends ASTNode {
+	/**
+	 * Replace {@code variable} with {@code expression} in AST.
+	 *
+	 * @param variable   The variable to be replaced
+	 * @param expression The expression that {@code variable} is replaced to
+	 * @return A dupulicated expression that is replaced with a given {@code expression}
+	 * @implNote The instance of any member must be immutable
+	 * @apiNote All variables match to the given one will be replaced with the given {@code expression}
+	 */
+	public abstract Expression replace(Variable variable, Expression expression);
 }