Theorem sbse ≪ | index | src | ≫ 

theorem sbse {x: nat} (a: nat) (A: set x) (B: set):
  $ x = a -> A == B $ >
  $ S[a / x] A == B $;
StepHypRefExpression
1 nfsv 
FS/ x B
2 hyp e 
x = a -> A == B
3 1, 2 sbseh 
S[a / x] 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)