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:   if (_isComparison(node)) {
      comparisons.add(node);
    } else if (_isBooleanOperation(node)) {
      comparisons.addAll(_extractComparisons(node as BinaryExpression));
    }
  }
  
  