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Theorem 0npi 9689
Description: The empty set is not a positive integer. (Contributed by NM, 26-Aug-1995.) (New usage is discouraged.)
Assertion
Ref Expression
0npi ¬ ∅ ∈ N

Proof of Theorem 0npi
StepHypRef Expression
1 eqid 2620 . 2 ∅ = ∅
2 elni 9683 . . . 4 (∅ ∈ N ↔ (∅ ∈ ω ∧ ∅ ≠ ∅))
32simprbi 480 . . 3 (∅ ∈ N → ∅ ≠ ∅)
43necon2bi 2821 . 2 (∅ = ∅ → ¬ ∅ ∈ N)
51, 4ax-mp 5 1 ¬ ∅ ∈ N
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3   = wceq 1481  wcel 1988  wne 2791  c0 3907  ωcom 7050  Ncnpi 9651
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1720  ax-4 1735  ax-5 1837  ax-6 1886  ax-7 1933  ax-9 1997  ax-10 2017  ax-11 2032  ax-12 2045  ax-13 2244  ax-ext 2600
This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1484  df-ex 1703  df-nf 1708  df-sb 1879  df-clab 2607  df-cleq 2613  df-clel 2616  df-nfc 2751  df-ne 2792  df-v 3197  df-dif 3570  df-sn 4169  df-ni 9679
This theorem is referenced by:  addasspi  9702  mulasspi  9704  distrpi  9705  addcanpi  9706  mulcanpi  9707  addnidpi  9708  ltapi  9710  ltmpi  9711  ordpipq  9749
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