anchor.diff:          return (() {
               $dart$core.bool doElse$11 = true;
               {
  -                Sequential tmp$12 = _$elements.collect(new dart$Callable(([$dart$core.Object $r]) => ($r as Entry).item));
  +                Sequential tmp$12 = _$elements.map(new dart$Callable(([$dart$core.Object $r]) => ($r as Entry).item)).sequence();
                   if (tmp$12 is Sequence) {
                       Sequence permutation;
                       permutation = tmp$12 as Sequence;
  
positive.code:         }
          return result;
      }
  }
  class Correspondence$keys$$anonymous$0_ implements Category {
      Correspondence $outer$ceylon$language$Correspondence;
  
negative.code:             $dart$core.bool doElse$11 = true;
              if (!(null == current)) {
                  doElse$11 = false;
                  return ($capture$set$choosing as Callable).f(current, element);
              }
              if (doElse$11) {
                  return element;
  