Theorem iexe ≪ | index | src | ≫

theorem iexe {x: nat} (a: nat) (b: wff x) (c: wff):
  $ x = a -> (b <-> c) $ >
  $ c -> E. x b $;

Step	Hyp	Ref	Expression
1		hyp e	x = a -> (b <-> c)
2	1	anwr	c /\ x = a -> (b <-> c)
3		anl	c /\ x = a -> c
4	2, 3	mpbird	c /\ x = a -> b
5	4	iexde	c -> E. x b

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_12)