Aha, that makes more sense. I interpret a type like `List[_ <: Number]` as a list with any kind of elements, whereas `List[T] forSome {type T <: Number}` makes

Aha, that makes more sense. I interpret a type like `List[_ <: Number]` as a list with any kind of elements, whereas `List[T] forSome {type T <: Number}` makes sense to be a list with a specific kind of elements, with the type of the elements constrained (of course, assuming that List is invariant).