?- valid(x > 0).

       No

       ?- valid(x >= 0).

       Yes

       ?- valid(exists(x, x > 0)).

       Yes

       ?- valid(forall(x, exists(y, 3*x + y > 2))).

       Yes

       ?- valid(x > 12 \/ x <= 12).

       Yes

       ?- valid(x >= 0 /\ exists(y, y = 5)).

       Yes

       ?- valid(x = 5 => 2*x = 10).

       Yes

       ?- valid(y > 1 /\ x = 3 /\ x + y < 19 => x + 19 > y).

       Yes