anchor.diff:        {Reachability? reachable}) {
       reachable ??= this.reachable;
       Map<Variable?, VariableModel<Variable, Type>> newVariableInfo =
  -        new Map<Variable?, VariableModel<Variable, Type>>.from(variableInfo);
  +        new Map<Variable?, VariableModel<Variable, Type>>.of(variableInfo);
       reference.storeInfo(newVariableInfo, model);
       return new FlowModel<Variable, Type>.withInfo(reachable, newVariableInfo);
     }
  
positive.code:           Type newType,
            TypeOperations<Variable, Type> typeOperations) {
      if (_typeListContains(typeOperations, types, newType)) return types;
      return new List<Type>.from(types)..add(newType);
    }
  
    /// Creates a new [VariableModel] object, unless it is equivalent to either
  
negative.code:             _assignedVariables._anywhere._written.contains(entry.key)) {
            continue;
          }
          (newKnownTypes ??= new Map<Variable, Type>.of(_knownTypes))[entry.key] =
              entry.value;
        }
        if (newKnownTypes != null) _knownTypes = newKnownTypes;
      }
  