About: (most generally, category theory, of an object F in a concrete category, with respect to a set X and a map i from X to the underlying set of F) Such that any map f from X to the underlying set of an object A in the same category as F induces a map \bar f from F to A which is compatible with f (i.e. such that f = \bar f \circ i).       Sponge   NotDistinct   Permalink