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descendant_type

In Deriscope terminology, a descendant type is a Deriscope Type D that has the following relationship to a given type T.
D is either the
child type of T or otherwise is the child type of a descendant type of T.

The above definition looks circular (the defined concept is part of the definition), but in reality is well defined if it is understood in the following inductive sense:

It follows from the definition that any child type of T (let's call it C) is a descendant type of T.
Then the definition dictates that any child type of C must also be a descendant type of T.
Proceeding inductively we recognize that the definition covers all types that belong in the "posterity" of T.