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Theorem nn0eln0 4369
 Description: A natural number is nonempty iff it contains the empty set. Although in constructive mathematics it is generally more natural to work with inhabited sets and ignore the whole concept of nonempty sets, in the specific case of natural numbers this theorem may be helpful in converting proofs which were written assuming excluded middle. (Contributed by Jim Kingdon, 28-Aug-2019.)
Assertion
Ref Expression
nn0eln0 (𝐴 ∈ ω → (∅ ∈ 𝐴𝐴 ≠ ∅))

Proof of Theorem nn0eln0
StepHypRef Expression
1 0elnn 4368 . 2 (𝐴 ∈ ω → (𝐴 = ∅ ∨ ∅ ∈ 𝐴))
2 noel 3256 . . . . 5 ¬ ∅ ∈ ∅
3 eleq2 2117 . . . . 5 (𝐴 = ∅ → (∅ ∈ 𝐴 ↔ ∅ ∈ ∅))
42, 3mtbiri 610 . . . 4 (𝐴 = ∅ → ¬ ∅ ∈ 𝐴)
5 nner 2224 . . . 4 (𝐴 = ∅ → ¬ 𝐴 ≠ ∅)
64, 52falsed 628 . . 3 (𝐴 = ∅ → (∅ ∈ 𝐴𝐴 ≠ ∅))
7 id 19 . . . 4 (∅ ∈ 𝐴 → ∅ ∈ 𝐴)
8 ne0i 3258 . . . 4 (∅ ∈ 𝐴𝐴 ≠ ∅)
97, 82thd 168 . . 3 (∅ ∈ 𝐴 → (∅ ∈ 𝐴𝐴 ≠ ∅))
106, 9jaoi 646 . 2 ((𝐴 = ∅ ∨ ∅ ∈ 𝐴) → (∅ ∈ 𝐴𝐴 ≠ ∅))
111, 10syl 14 1 (𝐴 ∈ ω → (∅ ∈ 𝐴𝐴 ≠ ∅))
 Colors of variables: wff set class Syntax hints:   → wi 4   ↔ wb 102   ∨ wo 639   = wceq 1259   ∈ wcel 1409   ≠ wne 2220  ∅c0 3252  ωcom 4341 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 103  ax-ia2 104  ax-ia3 105  ax-in1 554  ax-in2 555  ax-io 640  ax-5 1352  ax-7 1353  ax-gen 1354  ax-ie1 1398  ax-ie2 1399  ax-8 1411  ax-10 1412  ax-11 1413  ax-i12 1414  ax-bndl 1415  ax-4 1416  ax-13 1420  ax-14 1421  ax-17 1435  ax-i9 1439  ax-ial 1443  ax-i5r 1444  ax-ext 2038  ax-sep 3903  ax-nul 3911  ax-pow 3955  ax-pr 3972  ax-un 4198  ax-iinf 4339 This theorem depends on definitions:  df-bi 114  df-3an 898  df-tru 1262  df-nf 1366  df-sb 1662  df-clab 2043  df-cleq 2049  df-clel 2052  df-nfc 2183  df-ne 2221  df-ral 2328  df-rex 2329  df-v 2576  df-dif 2948  df-un 2950  df-in 2952  df-ss 2959  df-nul 3253  df-pw 3389  df-sn 3409  df-pr 3410  df-uni 3609  df-int 3644  df-suc 4136  df-iom 4342 This theorem is referenced by:  nnmord  6121
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