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Theorem phplem1 7223
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 4794 . . 3  |-  ( A  e.  om  ->  Ord  A )
2 nordeq 4542 . . . 4  |-  ( ( Ord  A  /\  B  e.  A )  ->  A  =/=  B )
3 disjsn2 3813 . . . 4  |-  ( A  =/=  B  ->  ( { A }  i^i  { B } )  =  (/) )
42, 3syl 16 . . 3  |-  ( ( Ord  A  /\  B  e.  A )  ->  ( { A }  i^i  { B } )  =  (/) )
51, 4sylan 458 . 2  |-  ( ( A  e.  om  /\  B  e.  A )  ->  ( { A }  i^i  { B } )  =  (/) )
6 undif4 3628 . . 3  |-  ( ( { A }  i^i  { B } )  =  (/)  ->  ( { A }  u.  ( A  \  { B } ) )  =  ( ( { A }  u.  A )  \  { B } ) )
7 df-suc 4529 . . . . 5  |-  suc  A  =  ( A  u.  { A } )
87equncomi 3437 . . . 4  |-  suc  A  =  ( { A }  u.  A )
98difeq1i 3405 . . 3  |-  ( suc 
A  \  { B } )  =  ( ( { A }  u.  A )  \  { B } )
106, 9syl6eqr 2438 . 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 set class
Syntax hints:    -> wi 4    /\ wa 359    = wceq 1649    e. wcel 1717    =/= wne 2551    \ cdif 3261    u. cun 3262    i^i cin 3263   (/)c0 3572   {csn 3758   Ord word 4522   suc csuc 4525   omcom 4786
This theorem is referenced by:  phplem2  7224
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1552  ax-5 1563  ax-17 1623  ax-9 1661  ax-8 1682  ax-13 1719  ax-14 1721  ax-6 1736  ax-7 1741  ax-11 1753  ax-12 1939  ax-ext 2369  ax-sep 4272  ax-nul 4280  ax-pr 4345  ax-un 4642
This theorem depends on definitions:  df-bi 178  df-or 360  df-an 361  df-3or 937  df-3an 938  df-tru 1325  df-ex 1548  df-nf 1551  df-sb 1656  df-eu 2243  df-mo 2244  df-clab 2375  df-cleq 2381  df-clel 2384  df-nfc 2513  df-ne 2553  df-ral 2655  df-rex 2656  df-rab 2659  df-v 2902  df-sbc 3106  df-dif 3267  df-un 3269  df-in 3271  df-ss 3278  df-pss 3280  df-nul 3573  df-if 3684  df-sn 3764  df-pr 3765  df-tp 3766  df-op 3767  df-uni 3959  df-br 4155  df-opab 4209  df-tr 4245  df-eprel 4436  df-po 4445  df-so 4446  df-fr 4483  df-we 4485  df-ord 4526  df-on 4527  df-lim 4528  df-suc 4529  df-om 4787
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