Theorem dtruALT 5358

Description: Alternate proof of dtru 5411 which requires more axioms but is shorter and may be easier to understand. Like dtruALT2 5340, it uses ax-pow 5335 rather than ax-pr 5402.

Assuming that ZF set theory is consistent, we cannot prove this theorem unless we specify that 𝑥 and 𝑦 be distinct. Specifically, Theorem spcev 3585 requires that 𝑥 must not occur in the subexpression ¬ 𝑦 = {∅} in step 4 nor in the subexpression ¬ 𝑦 = ∅ in step 9. The proof verifier will require that 𝑥 and 𝑦 be in a distinct variable group to ensure this. You can check this by deleting the $d statement in set.mm and rerunning the verifier, which will print a detailed explanation of the distinct variable violation. (Contributed by NM, 15-Jul-1994.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
dtruALT	⊢ ¬ ∀𝑥 𝑥 = 𝑦

Distinct variable group:   𝑥,𝑦

Proof of Theorem dtruALT

Step	Hyp	Ref	Expression
1		0inp0 5329	. . . 4 ⊢ (𝑦 = ∅ → ¬ 𝑦 = {∅})
2		p0ex 5354	. . . . 5 ⊢ {∅} ∈ V
3		eqeq2 2747	. . . . . 6 ⊢ (𝑥 = {∅} → (𝑦 = 𝑥 ↔ 𝑦 = {∅}))
4	3	notbid 318	. . . . 5 ⊢ (𝑥 = {∅} → (¬ 𝑦 = 𝑥 ↔ ¬ 𝑦 = {∅}))
5	2, 4	spcev 3585	. . . 4 ⊢ (¬ 𝑦 = {∅} → ∃𝑥 ¬ 𝑦 = 𝑥)
6	1, 5	syl 17	. . 3 ⊢ (𝑦 = ∅ → ∃𝑥 ¬ 𝑦 = 𝑥)
7		0ex 5277	. . . 4 ⊢ ∅ ∈ V
8		eqeq2 2747	. . . . 5 ⊢ (𝑥 = ∅ → (𝑦 = 𝑥 ↔ 𝑦 = ∅))
9	8	notbid 318	. . . 4 ⊢ (𝑥 = ∅ → (¬ 𝑦 = 𝑥 ↔ ¬ 𝑦 = ∅))
10	7, 9	spcev 3585	. . 3 ⊢ (¬ 𝑦 = ∅ → ∃𝑥 ¬ 𝑦 = 𝑥)
11	6, 10	pm2.61i 182	. 2 ⊢ ∃𝑥 ¬ 𝑦 = 𝑥
12		exnal 1827	. . 3 ⊢ (∃𝑥 ¬ 𝑦 = 𝑥 ↔ ¬ ∀𝑥 𝑦 = 𝑥)
13		eqcom 2742	. . . 4 ⊢ (𝑦 = 𝑥 ↔ 𝑥 = 𝑦)
14	13	albii 1819	. . 3 ⊢ (∀𝑥 𝑦 = 𝑥 ↔ ∀𝑥 𝑥 = 𝑦)
15	12, 14	xchbinx 334	. 2 ⊢ (∃𝑥 ¬ 𝑦 = 𝑥 ↔ ¬ ∀𝑥 𝑥 = 𝑦)
16	11, 15	mpbi 230	1 ⊢ ¬ ∀𝑥 𝑥 = 𝑦

Syntax hints:  ¬ wn 3  ∀wal 1538   = wceq 1540  ∃wex 1779  ∅c0 4308  {csn 4601

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-8 2110  ax-9 2118  ax-ext 2707  ax-sep 5266  ax-nul 5276  ax-pow 5335

This theorem depends on definitions:  df-bi 207  df-an 396  df-tru 1543  df-fal 1553  df-ex 1780  df-sb 2065  df-clab 2714  df-cleq 2727  df-clel 2809  df-ne 2933  df-v 3461  df-dif 3929  df-ss 3943  df-nul 4309  df-pw 4577  df-sn 4602

This theorem is referenced by: (None)