Theorem exmid01 4177

Description: Excluded middle is equivalent to saying any subset of {∅} is either ∅ or {∅}. (Contributed by BJ and Jim Kingdon, 18-Jun-2022.)

Assertion

Ref	Expression
exmid01	⊢ (EXMID ↔ ∀𝑥(𝑥 ⊆ {∅} → (𝑥 = ∅ ∨ 𝑥 = {∅})))

Proof of Theorem exmid01

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-exmid 4174	. 2 ⊢ (EXMID ↔ ∀𝑥(𝑥 ⊆ {∅} → DECID ∅ ∈ 𝑥))
2		df-dc 825	. . . . 5 ⊢ (DECID ∅ ∈ 𝑥 ↔ (∅ ∈ 𝑥 ∨ ¬ ∅ ∈ 𝑥))
3		orcom 718	. . . . . 6 ⊢ ((∅ ∈ 𝑥 ∨ ¬ ∅ ∈ 𝑥) ↔ (¬ ∅ ∈ 𝑥 ∨ ∅ ∈ 𝑥))
4		simpll 519	. . . . . . . . . . . . . 14 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → 𝑥 ⊆ {∅})
5		simpr 109	. . . . . . . . . . . . . 14 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → 𝑦 ∈ 𝑥)
6	4, 5	sseldd 3143	. . . . . . . . . . . . 13 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → 𝑦 ∈ {∅})
7		velsn 3593	. . . . . . . . . . . . 13 ⊢ (𝑦 ∈ {∅} ↔ 𝑦 = ∅)
8	6, 7	sylib 121	. . . . . . . . . . . 12 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → 𝑦 = ∅)
9	8, 5	eqeltrrd 2244	. . . . . . . . . . 11 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → ∅ ∈ 𝑥)
10		simplr 520	. . . . . . . . . . 11 ⊢ (((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) ∧ 𝑦 ∈ 𝑥) → ¬ ∅ ∈ 𝑥)
11	9, 10	pm2.65da 651	. . . . . . . . . 10 ⊢ ((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) → ¬ 𝑦 ∈ 𝑥)
12	11	eq0rdv 3453	. . . . . . . . 9 ⊢ ((𝑥 ⊆ {∅} ∧ ¬ ∅ ∈ 𝑥) → 𝑥 = ∅)
13	12	ex 114	. . . . . . . 8 ⊢ (𝑥 ⊆ {∅} → (¬ ∅ ∈ 𝑥 → 𝑥 = ∅))
14		noel 3413	. . . . . . . . 9 ⊢ ¬ ∅ ∈ ∅
15		eleq2 2230	. . . . . . . . 9 ⊢ (𝑥 = ∅ → (∅ ∈ 𝑥 ↔ ∅ ∈ ∅))
16	14, 15	mtbiri 665	. . . . . . . 8 ⊢ (𝑥 = ∅ → ¬ ∅ ∈ 𝑥)
17	13, 16	impbid1 141	. . . . . . 7 ⊢ (𝑥 ⊆ {∅} → (¬ ∅ ∈ 𝑥 ↔ 𝑥 = ∅))
18		ss1o0el1 4176	. . . . . . 7 ⊢ (𝑥 ⊆ {∅} → (∅ ∈ 𝑥 ↔ 𝑥 = {∅}))
19	17, 18	orbi12d 783	. . . . . 6 ⊢ (𝑥 ⊆ {∅} → ((¬ ∅ ∈ 𝑥 ∨ ∅ ∈ 𝑥) ↔ (𝑥 = ∅ ∨ 𝑥 = {∅})))
20	3, 19	syl5bb 191	. . . . 5 ⊢ (𝑥 ⊆ {∅} → ((∅ ∈ 𝑥 ∨ ¬ ∅ ∈ 𝑥) ↔ (𝑥 = ∅ ∨ 𝑥 = {∅})))
21	2, 20	syl5bb 191	. . . 4 ⊢ (𝑥 ⊆ {∅} → (DECID ∅ ∈ 𝑥 ↔ (𝑥 = ∅ ∨ 𝑥 = {∅})))
22	21	pm5.74i 179	. . 3 ⊢ ((𝑥 ⊆ {∅} → DECID ∅ ∈ 𝑥) ↔ (𝑥 ⊆ {∅} → (𝑥 = ∅ ∨ 𝑥 = {∅})))
23	22	albii 1458	. 2 ⊢ (∀𝑥(𝑥 ⊆ {∅} → DECID ∅ ∈ 𝑥) ↔ ∀𝑥(𝑥 ⊆ {∅} → (𝑥 = ∅ ∨ 𝑥 = {∅})))
24	1, 23	bitri 183	1 ⊢ (EXMID ↔ ∀𝑥(𝑥 ⊆ {∅} → (𝑥 = ∅ ∨ 𝑥 = {∅})))

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 103   ↔ wb 104   ∨ wo 698  DECID wdc 824  ∀wal 1341   = wceq 1343   ∈ wcel 2136   ⊆ wss 3116  ∅c0 3409  {csn 3576  EXMIDwem 4173

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147  ax-nul 4108

This theorem depends on definitions:  df-bi 116  df-dc 825  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2297  df-v 2728  df-dif 3118  df-in 3122  df-ss 3129  df-nul 3410  df-sn 3582  df-exmid 4174

This theorem is referenced by:  exmid1dc  4179  exmidn0m  4180  exmidsssn  4181  exmidpw  6874  exmidpweq  6875  exmidomni  7106  ss1oel2o  13873  exmidsbthrlem  13901  sbthom  13905