Thin categories #
A thin category (also known as a sparse category) is a category with at most one morphism between
each pair of objects.
Examples include posets, but also some indexing categories (diagrams) for special shapes of
To construct a category instance one only needs to specify the
as the axioms hold for free.
C is thin, then the category of functors to
C is also thin.
Further, to show two objects are isomorphic in a thin category, it suffices only to give a morphism
in each direction.