Term is currently instantiated to a ground term.
Tests whether X is completely instantiated, i.e. free of
unbound variables. In this context, mutable terms are
treated as nonground, so as to make
ground/1 a monotone
| ?- ground(9). yes | ?- ground(major(tom)). yes | ?- ground(a(1,Term,3)). no | ?- ground("a"). yes | ?- ground([1,foo(Term)]). no