Theorem Ifeq1 ≪ | index | src | ≫ 

theorem Ifeq1 (_p1 _p2: wff) (A B: set):
  $ (_p1 <-> _p2) -> If _p1 A B == If _p2 A B $;
StepHypRefExpression
1 id 
(_p1 <-> _p2) -> (_p1 <-> _p2)
2 1 Ifeq1d 
(_p1 <-> _p2) -> If _p1 A B == If _p2 A B

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp, itru), axs_pred_calc (ax_gen, ax_4, ax_5, ax_6, ax_7, ax_10, ax_11, ax_12), axs_set (elab, ax_8)