anchor.diff:    "function foo() {
       var val1_1 = x;
       var valrest2 = [y];
  -    if (undefined !== arguments['callee']['caller']['mv']) {
  +    if ('undefined' !== typeof arguments['callee']['caller']['mv']) {
           arguments['callee']['caller']['mv'] = valrest2;
       };
       return val1_1;
  
positive.code:     var b = mv1[0];
      return a + b;
  } finally {
      if (undefined === prevMv2) {
          delete arguments['callee']['mv'];
      } else {
          arguments['callee']['mv'] = prevMv2;
  
negative.code:             y = arguments[n1 + 1];
          };
      };
      var y = 'undefined' === typeof y ? 0 : y;
      return x + y;
  };
  return foo(1, 'y', 2);
  