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Theorem fin23lem25 9745
 Description: Lemma for fin23 9810. In a chain of finite sets, equinumerosity is equivalent to equality. (Contributed by Stefan O'Rear, 1-Nov-2014.)
Assertion
Ref Expression
fin23lem25 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ∧ (𝐴𝐵𝐵𝐴)) → (𝐴𝐵𝐴 = 𝐵))

Proof of Theorem fin23lem25
StepHypRef Expression
1 dfpss2 4061 . . . . . . . 8 (𝐴𝐵 ↔ (𝐴𝐵 ∧ ¬ 𝐴 = 𝐵))
2 php3 8702 . . . . . . . . . 10 ((𝐵 ∈ Fin ∧ 𝐴𝐵) → 𝐴𝐵)
3 sdomnen 8537 . . . . . . . . . 10 (𝐴𝐵 → ¬ 𝐴𝐵)
42, 3syl 17 . . . . . . . . 9 ((𝐵 ∈ Fin ∧ 𝐴𝐵) → ¬ 𝐴𝐵)
54ex 415 . . . . . . . 8 (𝐵 ∈ Fin → (𝐴𝐵 → ¬ 𝐴𝐵))
61, 5syl5bir 245 . . . . . . 7 (𝐵 ∈ Fin → ((𝐴𝐵 ∧ ¬ 𝐴 = 𝐵) → ¬ 𝐴𝐵))
76adantl 484 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin) → ((𝐴𝐵 ∧ ¬ 𝐴 = 𝐵) → ¬ 𝐴𝐵))
87expd 418 . . . . 5 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin) → (𝐴𝐵 → (¬ 𝐴 = 𝐵 → ¬ 𝐴𝐵)))
9 dfpss2 4061 . . . . . . . . 9 (𝐵𝐴 ↔ (𝐵𝐴 ∧ ¬ 𝐵 = 𝐴))
10 eqcom 2828 . . . . . . . . . . 11 (𝐵 = 𝐴𝐴 = 𝐵)
1110notbii 322 . . . . . . . . . 10 𝐵 = 𝐴 ↔ ¬ 𝐴 = 𝐵)
1211anbi2i 624 . . . . . . . . 9 ((𝐵𝐴 ∧ ¬ 𝐵 = 𝐴) ↔ (𝐵𝐴 ∧ ¬ 𝐴 = 𝐵))
139, 12bitri 277 . . . . . . . 8 (𝐵𝐴 ↔ (𝐵𝐴 ∧ ¬ 𝐴 = 𝐵))
14 php3 8702 . . . . . . . . . 10 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → 𝐵𝐴)
15 sdomnen 8537 . . . . . . . . . . 11 (𝐵𝐴 → ¬ 𝐵𝐴)
16 ensym 8557 . . . . . . . . . . 11 (𝐴𝐵𝐵𝐴)
1715, 16nsyl 142 . . . . . . . . . 10 (𝐵𝐴 → ¬ 𝐴𝐵)
1814, 17syl 17 . . . . . . . . 9 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → ¬ 𝐴𝐵)
1918ex 415 . . . . . . . 8 (𝐴 ∈ Fin → (𝐵𝐴 → ¬ 𝐴𝐵))
2013, 19syl5bir 245 . . . . . . 7 (𝐴 ∈ Fin → ((𝐵𝐴 ∧ ¬ 𝐴 = 𝐵) → ¬ 𝐴𝐵))
2120adantr 483 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin) → ((𝐵𝐴 ∧ ¬ 𝐴 = 𝐵) → ¬ 𝐴𝐵))
2221expd 418 . . . . 5 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin) → (𝐵𝐴 → (¬ 𝐴 = 𝐵 → ¬ 𝐴𝐵)))
238, 22jaod 855 . . . 4 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin) → ((𝐴𝐵𝐵𝐴) → (¬ 𝐴 = 𝐵 → ¬ 𝐴𝐵)))
24233impia 1113 . . 3 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ∧ (𝐴𝐵𝐵𝐴)) → (¬ 𝐴 = 𝐵 → ¬ 𝐴𝐵))
2524con4d 115 . 2 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ∧ (𝐴𝐵𝐵𝐴)) → (𝐴𝐵𝐴 = 𝐵))
26 eqeng 8542 . . 3 (𝐴 ∈ Fin → (𝐴 = 𝐵𝐴𝐵))
27263ad2ant1 1129 . 2 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ∧ (𝐴𝐵𝐵𝐴)) → (𝐴 = 𝐵𝐴𝐵))
2825, 27impbid 214 1 ((𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ∧ (𝐴𝐵𝐵𝐴)) → (𝐴𝐵𝐴 = 𝐵))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 208   ∧ wa 398   ∨ wo 843   ∧ w3a 1083   = wceq 1533   ∈ wcel 2110   ⊆ wss 3935   ⊊ wpss 3936   class class class wbr 5065   ≈ cen 8505   ≺ csdm 8507  Fincfn 8508 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1907  ax-6 1966  ax-7 2011  ax-8 2112  ax-9 2120  ax-10 2141  ax-11 2157  ax-12 2173  ax-ext 2793  ax-sep 5202  ax-nul 5209  ax-pow 5265  ax-pr 5329  ax-un 7460 This theorem depends on definitions:  df-bi 209  df-an 399  df-or 844  df-3or 1084  df-3an 1085  df-tru 1536  df-ex 1777  df-nf 1781  df-sb 2066  df-mo 2618  df-eu 2650  df-clab 2800  df-cleq 2814  df-clel 2893  df-nfc 2963  df-ne 3017  df-ral 3143  df-rex 3144  df-rab 3147  df-v 3496  df-sbc 3772  df-dif 3938  df-un 3940  df-in 3942  df-ss 3951  df-pss 3953  df-nul 4291  df-if 4467  df-pw 4540  df-sn 4567  df-pr 4569  df-tp 4571  df-op 4573  df-uni 4838  df-br 5066  df-opab 5128  df-tr 5172  df-id 5459  df-eprel 5464  df-po 5473  df-so 5474  df-fr 5513  df-we 5515  df-xp 5560  df-rel 5561  df-cnv 5562  df-co 5563  df-dm 5564  df-rn 5565  df-res 5566  df-ima 5567  df-ord 6193  df-on 6194  df-lim 6195  df-suc 6196  df-iota 6313  df-fun 6356  df-fn 6357  df-f 6358  df-f1 6359  df-fo 6360  df-f1o 6361  df-fv 6362  df-om 7580  df-er 8288  df-en 8509  df-dom 8510  df-sdom 8511  df-fin 8512 This theorem is referenced by:  fin23lem23  9747  fin1a2lem9  9829
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