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Theorem phplem1 7502
Description: Lemma for Pigeonhole Principle. If we join a natural number to itself minus an element, we end up with its successor minus the same element. (Contributed by NM, 25-May-1998.)
Assertion
Ref Expression
phplem1  |-  ( ( A  e.  om  /\  B  e.  A )  ->  ( { A }  u.  ( A  \  { B } ) )  =  ( suc  A  \  { B } ) )

Proof of Theorem phplem1
StepHypRef Expression
1 nnord 6496 . . 3  |-  ( A  e.  om  ->  Ord  A )
2 nordeq 4750 . . . 4  |-  ( ( Ord  A  /\  B  e.  A )  ->  A  =/=  B )
3 disjsn2 3949 . . . 4  |-  ( A  =/=  B  ->  ( { A }  i^i  { B } )  =  (/) )
42, 3syl 16 . . 3  |-  ( ( Ord  A  /\  B  e.  A )  ->  ( { A }  i^i  { B } )  =  (/) )
51, 4sylan 471 . 2  |-  ( ( A  e.  om  /\  B  e.  A )  ->  ( { A }  i^i  { B } )  =  (/) )
6 undif4 3747 . . 3  |-  ( ( { A }  i^i  { B } )  =  (/)  ->  ( { A }  u.  ( A  \  { B } ) )  =  ( ( { A }  u.  A )  \  { B } ) )
7 df-suc 4737 . . . . 5  |-  suc  A  =  ( A  u.  { A } )
87equncomi 3514 . . . 4  |-  suc  A  =  ( { A }  u.  A )
98difeq1i 3482 . . 3  |-  ( suc 
A  \  { B } )  =  ( ( { A }  u.  A )  \  { B } )
106, 9syl6eqr 2493 . 2  |-  ( ( { A }  i^i  { B } )  =  (/)  ->  ( { A }  u.  ( A  \  { B } ) )  =  ( suc 
A  \  { B } ) )
115, 10syl 16 1  |-  ( ( A  e.  om  /\  B  e.  A )  ->  ( { A }  u.  ( A  \  { B } ) )  =  ( suc  A  \  { B } ) )
Colors of variables: wff setvar class
Syntax hints:    -> wi 4    /\ wa 369    = wceq 1369    e. wcel 1756    =/= wne 2618    \ cdif 3337    u. cun 3338    i^i cin 3339   (/)c0 3649   {csn 3889   Ord word 4730   suc csuc 4733   omcom 6488
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1591  ax-4 1602  ax-5 1670  ax-6 1708  ax-7 1728  ax-8 1758  ax-9 1760  ax-10 1775  ax-11 1780  ax-12 1792  ax-13 1943  ax-ext 2423  ax-sep 4425  ax-nul 4433  ax-pr 4543  ax-un 6384
This theorem depends on definitions:  df-bi 185  df-or 370  df-an 371  df-3or 966  df-3an 967  df-tru 1372  df-ex 1587  df-nf 1590  df-sb 1701  df-eu 2257  df-mo 2258  df-clab 2430  df-cleq 2436  df-clel 2439  df-nfc 2577  df-ne 2620  df-ral 2732  df-rex 2733  df-rab 2736  df-v 2986  df-sbc 3199  df-dif 3343  df-un 3345  df-in 3347  df-ss 3354  df-pss 3356  df-nul 3650  df-if 3804  df-sn 3890  df-pr 3892  df-tp 3894  df-op 3896  df-uni 4104  df-br 4305  df-opab 4363  df-tr 4398  df-eprel 4644  df-po 4653  df-so 4654  df-fr 4691  df-we 4693  df-ord 4734  df-on 4735  df-lim 4736  df-suc 4737  df-om 6489
This theorem is referenced by:  phplem2  7503
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