anchor.diff:      }
       // prepare IsExpression
       if (node is! IsExpression) {
  -      _coverageMarker();
         return;
       }
       IsExpression isExpression = node;
  
positive.code:     }
      // prepare target "if" statement
      if (node is! IfStatement) {
        _coverageMarker();
        return;
      }
      var targetIfStatement = node as IfStatement;
      if (targetIfStatement.elseStatement != null) {
        _coverageMarker();
        return;
      }
      // prepare outer "if" statement
      var parent = targetIfStatement.parent;
      if (parent is Block) {
        if ((parent as Block).statements.length != 1) {
          _coverageMarker();
          return;
        }
        parent = parent.parent;
      }
      if (parent is! IfStatement) {
        _coverageMarker();
        return;
      }
      var outerIfStatement = parent as IfStatement;
      if (outerIfStatement.elseStatement != null) {
        _coverageMarker();
        return;
      }
      // prepare environment
  
negative.code:       } else if (!conflicts.contains('k')) {
          indexName = 'k';
        } else {
          return;
        }
      }
  