* [SET_THEORY,EXT] cardinality/2, equinumerous/2, random_subset/2, strict_subset/2, strict_superset/2, subset/2, superset/2 throw a type_error.
* [SET_THOERY,SC] Renamed minimal/2 -> minimal_set/2.
* [SET_THEORY,NEW] Added emptyset/1, struct_subset/2, strict_superset/2.