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Theorem cardidm 8823
Description: The cardinality function is idempotent. Proposition 10.11 of [TakeutiZaring] p. 85. (Contributed by Mario Carneiro, 7-Jan-2013.)
Assertion
Ref Expression
cardidm (card‘(card‘𝐴)) = (card‘𝐴)

Proof of Theorem cardidm
Dummy variable 𝑦 is distinct from all other variables.
StepHypRef Expression
1 cardid2 8817 . . . . . . . 8 (𝐴 ∈ dom card → (card‘𝐴) ≈ 𝐴)
21ensymd 8048 . . . . . . 7 (𝐴 ∈ dom card → 𝐴 ≈ (card‘𝐴))
3 entr 8049 . . . . . . . 8 ((𝑦𝐴𝐴 ≈ (card‘𝐴)) → 𝑦 ≈ (card‘𝐴))
43expcom 450 . . . . . . 7 (𝐴 ≈ (card‘𝐴) → (𝑦𝐴𝑦 ≈ (card‘𝐴)))
52, 4syl 17 . . . . . 6 (𝐴 ∈ dom card → (𝑦𝐴𝑦 ≈ (card‘𝐴)))
6 entr 8049 . . . . . . . 8 ((𝑦 ≈ (card‘𝐴) ∧ (card‘𝐴) ≈ 𝐴) → 𝑦𝐴)
76expcom 450 . . . . . . 7 ((card‘𝐴) ≈ 𝐴 → (𝑦 ≈ (card‘𝐴) → 𝑦𝐴))
81, 7syl 17 . . . . . 6 (𝐴 ∈ dom card → (𝑦 ≈ (card‘𝐴) → 𝑦𝐴))
95, 8impbid 202 . . . . 5 (𝐴 ∈ dom card → (𝑦𝐴𝑦 ≈ (card‘𝐴)))
109rabbidv 3220 . . . 4 (𝐴 ∈ dom card → {𝑦 ∈ On ∣ 𝑦𝐴} = {𝑦 ∈ On ∣ 𝑦 ≈ (card‘𝐴)})
1110inteqd 4512 . . 3 (𝐴 ∈ dom card → {𝑦 ∈ On ∣ 𝑦𝐴} = {𝑦 ∈ On ∣ 𝑦 ≈ (card‘𝐴)})
12 cardval3 8816 . . 3 (𝐴 ∈ dom card → (card‘𝐴) = {𝑦 ∈ On ∣ 𝑦𝐴})
13 cardon 8808 . . . 4 (card‘𝐴) ∈ On
14 oncardval 8819 . . . 4 ((card‘𝐴) ∈ On → (card‘(card‘𝐴)) = {𝑦 ∈ On ∣ 𝑦 ≈ (card‘𝐴)})
1513, 14mp1i 13 . . 3 (𝐴 ∈ dom card → (card‘(card‘𝐴)) = {𝑦 ∈ On ∣ 𝑦 ≈ (card‘𝐴)})
1611, 12, 153eqtr4rd 2696 . 2 (𝐴 ∈ dom card → (card‘(card‘𝐴)) = (card‘𝐴))
17 card0 8822 . . 3 (card‘∅) = ∅
18 ndmfv 6256 . . . 4 𝐴 ∈ dom card → (card‘𝐴) = ∅)
1918fveq2d 6233 . . 3 𝐴 ∈ dom card → (card‘(card‘𝐴)) = (card‘∅))
2017, 19, 183eqtr4a 2711 . 2 𝐴 ∈ dom card → (card‘(card‘𝐴)) = (card‘𝐴))
2116, 20pm2.61i 176 1 (card‘(card‘𝐴)) = (card‘𝐴)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4   = wceq 1523  wcel 2030  {crab 2945  c0 3948   cint 4507   class class class wbr 4685  dom cdm 5143  Oncon0 5761  cfv 5926  cen 7994  cardccrd 8799
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1762  ax-4 1777  ax-5 1879  ax-6 1945  ax-7 1981  ax-8 2032  ax-9 2039  ax-10 2059  ax-11 2074  ax-12 2087  ax-13 2282  ax-ext 2631  ax-sep 4814  ax-nul 4822  ax-pow 4873  ax-pr 4936  ax-un 6991
This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-3or 1055  df-3an 1056  df-tru 1526  df-ex 1745  df-nf 1750  df-sb 1938  df-eu 2502  df-mo 2503  df-clab 2638  df-cleq 2644  df-clel 2647  df-nfc 2782  df-ne 2824  df-ral 2946  df-rex 2947  df-rab 2950  df-v 3233  df-sbc 3469  df-dif 3610  df-un 3612  df-in 3614  df-ss 3621  df-pss 3623  df-nul 3949  df-if 4120  df-pw 4193  df-sn 4211  df-pr 4213  df-tp 4215  df-op 4217  df-uni 4469  df-int 4508  df-br 4686  df-opab 4746  df-mpt 4763  df-tr 4786  df-id 5053  df-eprel 5058  df-po 5064  df-so 5065  df-fr 5102  df-we 5104  df-xp 5149  df-rel 5150  df-cnv 5151  df-co 5152  df-dm 5153  df-rn 5154  df-res 5155  df-ima 5156  df-ord 5764  df-on 5765  df-iota 5889  df-fun 5928  df-fn 5929  df-f 5930  df-f1 5931  df-fo 5932  df-f1o 5933  df-fv 5934  df-er 7787  df-en 7998  df-card 8803
This theorem is referenced by:  oncard  8824  cardlim  8836  cardiun  8846  alephnbtwn2  8933  infenaleph  8952  dfac12k  9007  pwsdompw  9064  cardcf  9112  cfeq0  9116  cfflb  9119  alephval2  9432  cfpwsdom  9444  gch2  9535  tskcard  9641  hashcard  13184
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