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Theorem peano2nn 8188
 Description: Peano postulate: a successor of a positive integer is a positive integer. (Contributed by NM, 11-Jan-1997.) (Revised by Mario Carneiro, 17-Nov-2014.)
Assertion
Ref Expression
peano2nn (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℕ)

Proof of Theorem peano2nn
Dummy variables 𝑥 𝑦 𝑧 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 dfnn2 8178 . . . . . 6 ℕ = {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}
21eleq2i 2149 . . . . 5 (𝐴 ∈ ℕ ↔ 𝐴 {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)})
3 elintg 3664 . . . . 5 (𝐴 ∈ ℕ → (𝐴 {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧))
42, 3syl5bb 190 . . . 4 (𝐴 ∈ ℕ → (𝐴 ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧))
54ibi 174 . . 3 (𝐴 ∈ ℕ → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧)
6 vex 2613 . . . . . . . 8 𝑧 ∈ V
7 eleq2 2146 . . . . . . . . 9 (𝑥 = 𝑧 → (1 ∈ 𝑥 ↔ 1 ∈ 𝑧))
8 eleq2 2146 . . . . . . . . . 10 (𝑥 = 𝑧 → ((𝑦 + 1) ∈ 𝑥 ↔ (𝑦 + 1) ∈ 𝑧))
98raleqbi1dv 2562 . . . . . . . . 9 (𝑥 = 𝑧 → (∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥 ↔ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧))
107, 9anbi12d 457 . . . . . . . 8 (𝑥 = 𝑧 → ((1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥) ↔ (1 ∈ 𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧)))
116, 10elab 2746 . . . . . . 7 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ (1 ∈ 𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧))
1211simprbi 269 . . . . . 6 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} → ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧)
13 oveq1 5571 . . . . . . . 8 (𝑦 = 𝐴 → (𝑦 + 1) = (𝐴 + 1))
1413eleq1d 2151 . . . . . . 7 (𝑦 = 𝐴 → ((𝑦 + 1) ∈ 𝑧 ↔ (𝐴 + 1) ∈ 𝑧))
1514rspcva 2708 . . . . . 6 ((𝐴𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧) → (𝐴 + 1) ∈ 𝑧)
1612, 15sylan2 280 . . . . 5 ((𝐴𝑧𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}) → (𝐴 + 1) ∈ 𝑧)
1716expcom 114 . . . 4 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} → (𝐴𝑧 → (𝐴 + 1) ∈ 𝑧))
1817ralimia 2429 . . 3 (∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧 → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧)
195, 18syl 14 . 2 (𝐴 ∈ ℕ → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧)
20 nnre 8183 . . . 4 (𝐴 ∈ ℕ → 𝐴 ∈ ℝ)
21 1red 7266 . . . 4 (𝐴 ∈ ℕ → 1 ∈ ℝ)
2220, 21readdcld 7280 . . 3 (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℝ)
231eleq2i 2149 . . . 4 ((𝐴 + 1) ∈ ℕ ↔ (𝐴 + 1) ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)})
24 elintg 3664 . . . 4 ((𝐴 + 1) ∈ ℝ → ((𝐴 + 1) ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2523, 24syl5bb 190 . . 3 ((𝐴 + 1) ∈ ℝ → ((𝐴 + 1) ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2622, 25syl 14 . 2 (𝐴 ∈ ℕ → ((𝐴 + 1) ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2719, 26mpbird 165 1 (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℕ)
 Colors of variables: wff set class Syntax hints:   → wi 4   ∧ wa 102   ↔ wb 103   = wceq 1285   ∈ wcel 1434  {cab 2069  ∀wral 2353  ∩ cint 3656  (class class class)co 5564  ℝcr 7112  1c1 7114   + caddc 7116  ℕcn 8176 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-io 663  ax-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-10 1437  ax-11 1438  ax-i12 1439  ax-bndl 1440  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468  ax-i5r 1469  ax-ext 2065  ax-sep 3916  ax-cnex 7199  ax-resscn 7200  ax-1re 7202  ax-addrcl 7205 This theorem depends on definitions:  df-bi 115  df-3an 922  df-tru 1288  df-nf 1391  df-sb 1688  df-clab 2070  df-cleq 2076  df-clel 2079  df-nfc 2212  df-ral 2358  df-rex 2359  df-v 2612  df-un 2986  df-in 2988  df-ss 2995  df-sn 3422  df-pr 3423  df-op 3425  df-uni 3622  df-int 3657  df-br 3806  df-iota 4917  df-fv 4960  df-ov 5567  df-inn 8177 This theorem is referenced by:  peano2nnd  8191  nnind  8192  nnaddcl  8196  2nn  8330  3nn  8331  4nn  8332  5nn  8333  6nn  8334  7nn  8335  8nn  8336  9nn  8337  nneoor  8600  10nn  8643  fzonn0p1p1  9369  expp1  9650  facp1  9824  resqrexlemfp1  10114  resqrexlemcalc3  10121  nno  10531  nnoddm1d2  10535  rplpwr  10641  prmind2  10727  sqrt2irr  10766
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