anchor.diff:  
       if (_contradictions.isEmpty) {
         Set<Expression> set = (binaryExpression != null
  -          ? _extractComparisons(testingExpression)
  +          ? _extractComparisons(testingExpression as BinaryExpression)
             : {testingExpression})
           ..addAll(truths)
           ..addAll(negations);
  
positive.code:           return;
          }
  
          final BinaryExpression otherExpression = c;
  
          final String bcLeftOperand = otherExpression.leftOperand.toString();
          final String bcRightOperand = otherExpression.rightOperand.toString();
  
negative.code:         LinkedHashSet.identity();
  
      if (testingExpression is SimpleIdentifier) {
        SimpleIdentifier identifier = testingExpression as SimpleIdentifier;
        bool sameIdentifier(n) =>
            n is SimpleIdentifier && identifier.staticElement == n.staticElement;
        if (negations.any(sameIdentifier)) {
          SimpleIdentifier otherIdentifier =
              negations.firstWhere(sameIdentifier) as SimpleIdentifier;
          contradictions
              .add(ContradictoryComparisons(otherIdentifier, identifier));
        }
  