> An HKT is the type of a type constructor. That is a ("normal") kind `* -> *`. A Java `List<_>` or `Set<T>` would be a "normal/concrete" type constructor. In

> An HKT is the type of a type constructor. That is a ("normal") kind `* -> *`. A Java `List<_>` or `Set<T>` would be a "normal/concrete" type constructor. In your example the problem is that `C` is a "generic" type constructor, so it has a higher (-order) kind, that takes a type constructor as argument (like `List<_>` or `Set<_>`) and constructs a type from this: `(* -> *) -> *`.