Theorem ssasym | index | src |

theorem ssasym (A B: set): $ A C_ B -> B C_ A -> A == B $;
StepHypRefExpression
1 ian
(x e. A -> x e. B) -> (x e. B -> x e. A) -> (x e. A -> x e. B) /\ (x e. B -> x e. A)
2 1 conv iff
(x e. A -> x e. B) -> (x e. B -> x e. A) -> (x e. A <-> x e. B)
3 2 al2imi
A. x (x e. A -> x e. B) -> A. x (x e. B -> x e. A) -> A. x (x e. A <-> x e. B)
4 3 conv eqs, subset
A C_ B -> B C_ A -> A == B

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp), axs_pred_calc (ax_gen, ax_4)