Theorem elxab | index | src |

theorem elxab (A C: set) (a b: nat) {x: nat} (B: set x):
  $ x = a -> B == C $ >
  $ a, b e. X\ x e. A, B <-> a e. A /\ b e. C $;
StepHypRefExpression
1 bitr
(a, b e. X\ x e. A, B <-> a e. A /\ b e. S[a / x] B) -> (a e. A /\ b e. S[a / x] B <-> a e. A /\ b e. C) -> (a, b e. X\ x e. A, B <-> a e. A /\ b e. C)
2 elxabs
a, b e. X\ x e. A, B <-> a e. A /\ b e. S[a / x] B
3 1, 2 ax_mp
(a e. A /\ b e. S[a / x] B <-> a e. A /\ b e. C) -> (a, b e. X\ x e. A, B <-> a e. A /\ b e. C)
4 eleq2
S[a / x] B == C -> (b e. S[a / x] B <-> b e. C)
5 hyp h
x = a -> B == C
6 5 sbse
S[a / x] B == C
7 4, 6 ax_mp
b e. S[a / x] B <-> b e. C
8 7 aneq2i
a e. A /\ b e. S[a / x] B <-> a e. A /\ b e. C
9 3, 8 ax_mp
a, b e. X\ x e. A, B <-> a e. A /\ b e. 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), axs_set (elab, ax_8), axs_the (theid, the0), axs_peano (peano1, peano2, peano5, addeq, muleq, add0, addS, mul0, mulS)