direct container type
In Deriscope terminology, a Deriscope TypeA is called a direct container type of a type B if A is a container type of B and no other type T exists in between.
It follows that then B is a direct subtype of A
As an example, the following two statements hold:
1) The type Tradable is a direct container type of the type Bond
2) The type Tradable is not a direct container type of the type Zero Bond