direct subtype

In Deriscope terminology, a Deriscope TypeB is called a direct subtype of a type A if B is a subtype of A and no other type T exists in between.

It follows that then A is a direct container type of B

As an example, the following two statements hold:
1) The type Bond is a direct subtype of the type Tradable
2) The type Zero Bond is not a direct subtype of the type Tradable