diff --git a/docs/Chap15/15.4.md b/docs/Chap15/15.4.md
index 7ff4c77375..c42ca709f4 100755
--- a/docs/Chap15/15.4.md
+++ b/docs/Chap15/15.4.md
@@ -32,8 +32,8 @@ MEMOIZED-LCS-LENGTH(X, Y, i, j)
     if i == 0 or j == 0
         return c[i, j] = 0
     if x[i] == y[j]
-        return c[i, j] = LCS-LENGTH(X, Y, i - 1, j - 1) + 1
-    return c[i, j] = max(LCS-LENGTH(X, Y, i - 1, j), LCS-LENGTH(X, Y, i, j - 1))
+        return c[i, j] = MEMOIZED-LCS-LENGTH(X, Y, i - 1, j - 1) + 1
+    return c[i, j] = max(MEMOIZED-LCS-LENGTH(X, Y, i - 1, j), MEMOIZED-LCS-LENGTH(X, Y, i, j - 1))
 ```
 
 ## 15.4-4