anchor.diff:    CalculatorElement.created() : super.created();
   
     void number(Event e, var detail, ButtonElement target) {
  +    if (solved) return;
       if (decimals > 0) {
         current = current + dec(multi) * dec(target.value) / dec(decimals);
         decimals *= 10;
  
positive.code: 
    int decimals = 0;
    int multi = 1;
  
    BinaryOperation operation;
    var operands = new Queue<Term>();
  
negative.code:       throw 'Try again later, trying to figure out what went wrong.';
      } else {
        current = operands.removeFirst().evaluate();
        solved = true;
      }
    }
  
    void _prepareNextTerm(BinaryOperation operation) {
      operands.add(new NullaryTerm(current));
      operations.add(operation);
      solved = false;
      current = dec(0);
      decimals = 0;
      multi = 1;
  