anchor.diff:    bool get isReachable => true;
   
     @override
  +  TypeOperations<Variable, Type> get typeOperations => _typeOperations;
  +
  +  @override
     void asExpression_end(Expression subExpression, Type type) {}
   
     @override
  
positive.code:   @override
    bool get isReachable =>
        _wrap('isReachable', () => _wrapped.isReachable, isQuery: true);
  
    @override
    void asExpression_end(Expression subExpression, Type type) {
  
negative.code:   /// Return `true` if the current state is reachable.
    bool get isReachable;
  
    TypeOperations<Variable, Type> get typeOperations;
  
    /// Call this method after visiting an "as" expression.
    ///
    /// [subExpression] should be the expression to which the "as" check was
  