I think we should have an ISO committee to come up with a predicate naming convention to make such ambiguous (and short) predicate names unambiguous and elegant 
Maybe “delete_members_if_both_ground”, etc.
Gotta love the double negative in the source code (presumably to reduce garbage-collection activity).
Surely its arguments are in the wrong order anyway - should have the Element as the first argument, as with e.g. select/3