2 `((?x. !y. P(x) <=> P(y)) <=> ((?x. Q(x)) <=> (!y. Q(y)))) <=>
3 ((?x. !y. Q(x) <=> Q(y)) <=> ((?x. P(x)) <=> (!y. P(y))))`;;
6 `(!x y z. P x y /\ P y z ==> P x z) /\
7 (!x y z. Q x y /\ Q y z ==> Q x z) /\
8 (!x y. P x y ==> P y x) /\
10 ==> (!x y. P x y) \/ (!x y. Q x y)`;;
14 (!x y z. x <= y /\ y <= z ==> x <= z) /\
15 (!x y. f(x) <= y <=> x <= g(y))
16 ==> (!x y. x <= y ==> f(x) <= f(y)) /\
17 (!x y. x <= y ==> g(x) <= g(y))`;;
21 (!x y z. R x y /\ R y z ==> R x z) /\
22 (!x y. R (f x) y <=> R x (g y))
23 ==> (!x y. R x y ==> R (f x) (f y)) /\
24 (!x y. R x y ==> R (g x) (g y))`;;
26 MESON[] `(?!x. g(f x) = x) <=> (?!y. f(g y) = y)`;;
28 MESON [ADD_ASSOC; ADD_SYM] `m + (n + p) = n + (m + p)`;;