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Theorem ord0 4128
 Description: The empty set is an ordinal class. (Contributed by NM, 11-May-1994.)
Assertion
Ref Expression
ord0 Ord ∅

Proof of Theorem ord0
StepHypRef Expression
1 tr0 3865 . 2 Tr ∅
2 ral0 3322 . 2 𝑥 ∈ ∅ Tr 𝑥
3 dford3 4104 . 2 (Ord ∅ ↔ (Tr ∅ ∧ ∀𝑥 ∈ ∅ Tr 𝑥))
41, 2, 3mpbir2an 849 1 Ord ∅
 Colors of variables: wff set class Syntax hints:  ∀wral 2306  ∅c0 3224  Tr wtr 3854  Ord word 4099 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022 This theorem depends on definitions:  df-bi 110  df-tru 1246  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-nfc 2167  df-ral 2311  df-v 2559  df-dif 2920  df-in 2924  df-ss 2931  df-nul 3225  df-pw 3361  df-uni 3581  df-tr 3855  df-iord 4103 This theorem is referenced by:  0elon  4129  ordtriexmidlem  4245  2ordpr  4249  smo0  5913
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