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Theorem fidifsnid 6849
Description: If we remove a single element from a finite set then put it back in, we end up with the original finite set. This strengthens difsnss 3726 from subset to equality when the set is finite. (Contributed by Jim Kingdon, 9-Sep-2021.)
Assertion
Ref Expression
fidifsnid  |-  ( ( A  e.  Fin  /\  B  e.  A )  ->  ( ( A  \  { B } )  u. 
{ B } )  =  A )

Proof of Theorem fidifsnid
Dummy variables  x  y are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 fidceq 6847 . . . 4  |-  ( ( A  e.  Fin  /\  x  e.  A  /\  y  e.  A )  -> DECID  x  =  y )
213expb 1199 . . 3  |-  ( ( A  e.  Fin  /\  ( x  e.  A  /\  y  e.  A
) )  -> DECID  x  =  y
)
32ralrimivva 2552 . 2  |-  ( A  e.  Fin  ->  A. x  e.  A  A. y  e.  A DECID  x  =  y
)
4 dcdifsnid 6483 . 2  |-  ( ( A. x  e.  A  A. y  e.  A DECID  x  =  y  /\  B  e.  A )  ->  (
( A  \  { B } )  u.  { B } )  =  A )
53, 4sylan 281 1  |-  ( ( A  e.  Fin  /\  B  e.  A )  ->  ( ( A  \  { B } )  u. 
{ B } )  =  A )
Colors of variables: wff set class
Syntax hints:    -> wi 4    /\ wa 103  DECID wdc 829    = wceq 1348    e. wcel 2141   A.wral 2448    \ cdif 3118    u. cun 3119   {csn 3583   Fincfn 6718
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 609  ax-in2 610  ax-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-10 1498  ax-11 1499  ax-i12 1500  ax-bndl 1502  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-13 2143  ax-14 2144  ax-ext 2152  ax-sep 4107  ax-nul 4115  ax-pow 4160  ax-pr 4194  ax-un 4418  ax-setind 4521  ax-iinf 4572
This theorem depends on definitions:  df-bi 116  df-dc 830  df-3or 974  df-3an 975  df-tru 1351  df-nf 1454  df-sb 1756  df-eu 2022  df-mo 2023  df-clab 2157  df-cleq 2163  df-clel 2166  df-nfc 2301  df-ne 2341  df-ral 2453  df-rex 2454  df-v 2732  df-sbc 2956  df-dif 3123  df-un 3125  df-in 3127  df-ss 3134  df-nul 3415  df-pw 3568  df-sn 3589  df-pr 3590  df-op 3592  df-uni 3797  df-int 3832  df-br 3990  df-opab 4051  df-tr 4088  df-id 4278  df-iord 4351  df-on 4353  df-suc 4356  df-iom 4575  df-xp 4617  df-rel 4618  df-cnv 4619  df-co 4620  df-dm 4621  df-rn 4622  df-iota 5160  df-fun 5200  df-fn 5201  df-f 5202  df-f1 5203  df-fo 5204  df-f1o 5205  df-fv 5206  df-en 6719  df-fin 6721
This theorem is referenced by:  findcard2  6867  findcard2s  6868  xpfi  6907  fisseneq  6909  zfz1isolem1  10775
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