[lalaithion]

System.Object is a type of all objects, NOT a type of all types. That is, all objects are System.Object. If one has a class Foo, then every object of type Foo is also of type System.Object. But what is the type of Foo itself? Not of an instance of Foo, but Foo itself. In the languages this paper is about, the type system can recurse upon itself, allowing types themselves to have type. It’s sort of like C#’s System.Type, except System.Type is a class that holds type information for runtime type inspection, whereas the type of types in this paper is for compile-time generics that can abstract over not just types but the types of types as well.