Theorem sbe ≪ | index | src | ≫ 

theorem sbe {x: nat} (a: nat) (b: wff x) (c: wff):
  $ x = a -> (b <-> c) $ >
  $ [a / x] b <-> c $;
StepHypRefExpression
1 nfv 
F/ x c
2 hyp e 
x = a -> (b <-> c)
3 1, 2 sbeh 
[a / x] b <-> c

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)