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Theorem pssdifn0 4369
Description: A proper subclass has a nonempty difference. (Contributed by NM, 3-May-1994.)
Assertion
Ref Expression
pssdifn0 ((𝐴𝐵𝐴𝐵) → (𝐵𝐴) ≠ ∅)

Proof of Theorem pssdifn0
StepHypRef Expression
1 ssdif0 4367 . . . 4 (𝐵𝐴 ↔ (𝐵𝐴) = ∅)
2 eqss 3997 . . . . 5 (𝐴 = 𝐵 ↔ (𝐴𝐵𝐵𝐴))
32simplbi2 499 . . . 4 (𝐴𝐵 → (𝐵𝐴𝐴 = 𝐵))
41, 3biimtrrid 242 . . 3 (𝐴𝐵 → ((𝐵𝐴) = ∅ → 𝐴 = 𝐵))
54necon3d 2958 . 2 (𝐴𝐵 → (𝐴𝐵 → (𝐵𝐴) ≠ ∅))
65imp 405 1 ((𝐴𝐵𝐴𝐵) → (𝐵𝐴) ≠ ∅)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wa 394   = wceq 1533  wne 2937  cdif 3946  wss 3949  c0 4326
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1905  ax-6 1963  ax-7 2003  ax-8 2100  ax-9 2108  ax-ext 2699
This theorem depends on definitions:  df-bi 206  df-an 395  df-tru 1536  df-fal 1546  df-ex 1774  df-sb 2060  df-clab 2706  df-cleq 2720  df-clel 2806  df-ne 2938  df-v 3475  df-dif 3952  df-in 3956  df-ss 3966  df-nul 4327
This theorem is referenced by:  pssdif  4370  tz7.7  6400  domdifsn  9085  inf3lem3  9661  isf32lem6  10389  fclscf  23949  flimfnfcls  23952  lebnumlem1  24907  lebnumlem2  24908  lebnumlem3  24909  ig1peu  26129  ig1pdvds  26134  qsidomlem2  33194  qsdrng  33233  divrngidl  37534
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