anchor.diff:      final futureOrFutureOrVoidType =
           futureOrType.instantiate([futureOrVoidType]);
   
  -    final orderedTops = [
  +    var orderedTops = [
         // Lower index, so lower Top
         voidType,
         dynamicType,
  
positive.code:       doubleType,
        intType,
        numType,
        objectType
      ];
  
      for (final formOfNull in equivalents) {
  
negative.code:     _checkOrdinarySubtypeMatch(dynamicType, dynamicType, [T], covariant: true);
      _checkOrdinarySubtypeMatch(objectType, dynamicType, [T], covariant: true);
      _checkOrdinarySubtypeMatch(nullType, dynamicType, [T], covariant: true);
      _checkOrdinarySubtypeMatch(
        _functionType(required: [intType], returns: stringType),
        dynamicType,
        [T],
        covariant: true,
      );
    }
  
    void test_rhs_object() {
  