anchor.diff:    }
     
     void _subsetConstraint(TypeIdentifier a, TypeIdentifier b) {
  -
  -   
  -      if (a.toString() == '#_DoubleLinkedQueueEntrySentinel._next' &&
  -          b.toString() == '#{entry._next}') {
  -       print('foo'); 
  -       debugStop = true;
  -      }
  -      
       if (a != b)
         foreach(a).update((AbstractType type) => types.put(b, type));
  -    
  -    
  -    if (a.toString() == '#_DoubleLinkedQueueEntrySentinel._next' &&
  -        b.toString() == '#{entry._next}') {
  -      debugStop = false;
  -    }
  -
     }
     
     AbstractType _getAbstractType(Name className, LibraryElement library, SourceElement source){
  
positive.code:     _filters[func] = filter;
      
      bool reset;
      List current_types = types;
      do {
        reset = false;    
        for(AbstractType type in current_types){
          if (filter == null || filter(type)) {
            func(type);
    
            if (_types.length != current_types.length){
              //Changes has been made, so make another notify loop.
              reset = true;
              break;
            }
          }
        }
      } while(reset);
  
negative.code: import 'util.dart';
  import 'dart:collection';
  
  class ConstraintAnalysis {
    TypeMap typeMap;
    
  