  var util = {};
  
  /**
-@@ -118,3 +115,21 @@ util.pump = function(readableStream, writableStream, callback) {};
+@@ -118,3 +115,27 @@ util.pump = function(readableStream, writableStream, callback) {};
   * @param {Function} superConstructor
   */
  util.inherits = function(constructor, superConstructor) {};

+ * @param {*} arg
+ */
+util.isBoolean = function (arg) {};
diff --git a/vm.js b/vm.js
index 8abe142..3e8289a 100644
--- a/vm.js

 
 /**
diff --git a/util.js b/util.js
index ab1288b..73b1ea7 100644
--- a/util.js
+++ b/util.js
@@ -28,9 +28,6 @@
