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Theorem el1o 6440
Description: Membership in ordinal one. (Contributed by NM, 5-Jan-2005.)
Assertion
Ref Expression
el1o (𝐴 ∈ 1o𝐴 = ∅)

Proof of Theorem el1o
StepHypRef Expression
1 df1o2 6432 . . 3 1o = {∅}
21eleq2i 2244 . 2 (𝐴 ∈ 1o𝐴 ∈ {∅})
3 0ex 4132 . . 3 ∅ ∈ V
43elsn2 3628 . 2 (𝐴 ∈ {∅} ↔ 𝐴 = ∅)
52, 4bitri 184 1 (𝐴 ∈ 1o𝐴 = ∅)
Colors of variables: wff set class
Syntax hints:  wb 105   = wceq 1353  wcel 2148  c0 3424  {csn 3594  1oc1o 6412
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 614  ax-in2 615  ax-io 709  ax-5 1447  ax-7 1448  ax-gen 1449  ax-ie1 1493  ax-ie2 1494  ax-8 1504  ax-10 1505  ax-11 1506  ax-i12 1507  ax-bndl 1509  ax-4 1510  ax-17 1526  ax-i9 1530  ax-ial 1534  ax-i5r 1535  ax-ext 2159  ax-nul 4131
This theorem depends on definitions:  df-bi 117  df-tru 1356  df-nf 1461  df-sb 1763  df-clab 2164  df-cleq 2170  df-clel 2173  df-nfc 2308  df-v 2741  df-dif 3133  df-un 3135  df-nul 3425  df-sn 3600  df-suc 4373  df-1o 6419
This theorem is referenced by:  0lt1o  6443  map0e  6688  map1  6814  omp1eomlem  7095  ctmlemr  7109  ctssdclemn0  7111  exmidfodomrlemeldju  7200  exmidfodomrlemreseldju  7201  pw1on  7227  1tonninf  10442
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