Theorem dfss ≪ | index | src | ≫

theorem dfss (A B: set) {x: nat}: $ A C_ B <-> A. x (x e. A -> x e. B) $;

Step	Hyp	Ref	Expression
1		biid	A C_ B <-> A C_ B
2	1	conv subset	A C_ B <-> A. x (x e. A -> x e. B)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)