class Thing
    class Creature extends Thing
    class Human extends Creature

    abstract class Two {
      def bi[A, B <: A](a: A, b: B): String
      def bis[A, B <: A](a: A, b: B): A
    }

    class Twos extends Two {
      // CORRECT
      def bi[Creature, Human](a: Creature, b: Human): String = { "asd" }

      //ERROR: class type required but Creature found
      def bis[Creature, Human](a: Creature, b: Human): Creature = { new Creature }
    }