Theorem eqseq2 ≪ | index | src | ≫

theorem eqseq2 (A _B1 _B2: set): $ _B1 == _B2 -> (A == _B1 <-> A == _B2) $;

Step	Hyp	Ref	Expression
1		id	_B1 == _B2 -> _B1 == _B2
2	1	eqseq2d	_B1 == _B2 -> (A == _B1 <-> A == _B2)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp), axs_pred_calc (ax_gen, ax_4, ax_5, ax_6, ax_7, ax_10, ax_12), axs_set (ax_8)