# MATH introduce logical implication
[hear] (intro =>);
[hear] (define => /
? x /
? y /
not /
and (x) (not / y));
[hear] (=> (true) (true));
[hear] (not / => (true) (false));
[hear] (=> (false) (true));
[hear] (=> (false) (false));
[hear] (forall
(? x /
forall
(? y /
=> (=> (x) (y)) (=> (not / y) (not / x)))));