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Theorem onprc 6688
Description: No set contains all ordinal numbers. Proposition 7.13 of [TakeutiZaring] p. 38, but without using the Axiom of Regularity. This is also known as the Burali-Forti paradox (remark in [Enderton] p. 194). In 1897, Cesare Burali-Forti noticed that since the "set" of all ordinal numbers is an ordinal class (ordon 6686), it must be both an element of the set of all ordinal numbers yet greater than every such element. ZF set theory resolves this paradox by not allowing the class of all ordinal numbers to be a set (so instead it is a proper class). Here we prove the denial of its existence. (Contributed by NM, 18-May-1994.)
Assertion
Ref Expression
onprc ¬ On ∈ V

Proof of Theorem onprc
StepHypRef Expression
1 ordon 6686 . . 3 Ord On
2 ordirr 5492 . . 3 (Ord On → ¬ On ∈ On)
31, 2ax-mp 5 . 2 ¬ On ∈ On
4 elong 5482 . . 3 (On ∈ V → (On ∈ On ↔ Ord On))
51, 4mpbiri 243 . 2 (On ∈ V → On ∈ On)
63, 5mto 183 1 ¬ On ∈ V
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wcel 1937  Vcvv 3066  Ord word 5473  Oncon0 5474
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1698  ax-4 1711  ax-5 1789  ax-6 1836  ax-7 1883  ax-8 1939  ax-9 1946  ax-10 1965  ax-11 1970  ax-12 1983  ax-13 2137  ax-ext 2485  ax-sep 4558  ax-nul 4567  ax-pr 4680  ax-un 6659
This theorem depends on definitions:  df-bi 192  df-or 379  df-an 380  df-3or 1022  df-3an 1023  df-tru 1471  df-ex 1693  df-nf 1697  df-sb 1829  df-eu 2357  df-mo 2358  df-clab 2492  df-cleq 2498  df-clel 2501  df-nfc 2635  df-ne 2677  df-ral 2796  df-rex 2797  df-rab 2800  df-v 3068  df-sbc 3292  df-dif 3429  df-un 3431  df-in 3433  df-ss 3440  df-pss 3442  df-nul 3758  df-if 3909  df-sn 3996  df-pr 3998  df-tp 4000  df-op 4002  df-uni 4229  df-br 4435  df-opab 4494  df-tr 4531  df-eprel 4791  df-po 4801  df-so 4802  df-fr 4839  df-we 4841  df-ord 5477  df-on 5478
This theorem is referenced by:  ordeleqon  6692  ssonprc  6696  sucon  6712  orduninsuc  6747  omelon2  6781  tfr2b  7191  tz7.48-3  7238  infensuc  7834  zorn2lem4  9014  noprc  30721
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