Theorem ax8 211

Description: Axiom of Equality. Axiom scheme C8' in [Megill] p. 448 (p. 16 of the preprint). Also appears as Axiom C7 of [Monk2] p. 105. (Contributed by Mario Carneiro, 10-Oct-2014.)

Hypotheses

Ref	Expression
ax8.1	⊢ A:α
ax8.2	⊢ B:α
ax8.3	⊢ C:α

Assertion

Ref	Expression
ax8	⊢ ⊤⊧[[A = B] ⇒ [[A = C] ⇒ [B = C]]]

Proof of Theorem ax8

Step	Hyp	Ref	Expression
1		ax8.2	. . . . 5 ⊢ B:α
2		ax8.1	. . . . . 6 ⊢ A:α
3	2, 1	weqi 76	. . . . . . 7 ⊢ [A = B]:∗
4		ax8.3	. . . . . . . 8 ⊢ C:α
5	2, 4	weqi 76	. . . . . . 7 ⊢ [A = C]:∗
6	3, 5	simpl 22	. . . . . 6 ⊢ ([A = B], [A = C])⊧[A = B]
7	2, 6	eqcomi 79	. . . . 5 ⊢ ([A = B], [A = C])⊧[B = A]
8	3, 5	simpr 23	. . . . 5 ⊢ ([A = B], [A = C])⊧[A = C]
9	1, 7, 8	eqtri 95	. . . 4 ⊢ ([A = B], [A = C])⊧[B = C]
10	9	ex 158	. . 3 ⊢ [A = B]⊧[[A = C] ⇒ [B = C]]
11		wtru 43	. . 3 ⊢ ⊤:∗
12	10, 11	adantl 56	. 2 ⊢ (⊤, [A = B])⊧[[A = C] ⇒ [B = C]]
13	12	ex 158	1 ⊢ ⊤⊧[[A = B] ⇒ [[A = C] ⇒ [B = C]]]

Syntax hints:   = ke 7  ⊤kt 8  [kbr 9  kct 10  ⊧wffMMJ2 11  wffMMJ2t 12   ⇒ tim 121

This theorem was proved from axioms:  ax-syl 15  ax-jca 17  ax-simpl 20  ax-simpr 21  ax-id 24  ax-trud 26  ax-cb1 29  ax-cb2 30  ax-wctl 31  ax-wctr 32  ax-weq 40  ax-refl 42  ax-eqmp 45  ax-ded 46  ax-wct 47  ax-wc 49  ax-ceq 51  ax-wv 63  ax-wl 65  ax-beta 67  ax-distrc 68  ax-leq 69  ax-distrl 70  ax-wov 71  ax-eqtypi 77  ax-eqtypri 80  ax-hbl1 103  ax-17 105  ax-inst 113

This theorem depends on definitions:  df-ov 73  df-an 128  df-im 129

This theorem is referenced by: (None)