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Theorem ordun 4494
Description: The maximum (i.e. union) of two ordinals is ordinal. Exercise 12 of [TakeutiZaring] p. 40. (Contributed by NM, 28-Nov-2003.)
Assertion
Ref Expression
ordun  |-  ( ( Ord  A  /\  Ord  B )  ->  Ord  ( A  u.  B ) )

Proof of Theorem ordun
StepHypRef Expression
1 eqid 2283 . . 3  |-  ( A  u.  B )  =  ( A  u.  B
)
2 ordequn 4493 . . 3  |-  ( ( Ord  A  /\  Ord  B )  ->  ( ( A  u.  B )  =  ( A  u.  B )  ->  (
( A  u.  B
)  =  A  \/  ( A  u.  B
)  =  B ) ) )
31, 2mpi 16 . 2  |-  ( ( Ord  A  /\  Ord  B )  ->  ( ( A  u.  B )  =  A  \/  ( A  u.  B )  =  B ) )
4 ordeq 4399 . . . 4  |-  ( ( A  u.  B )  =  A  ->  ( Ord  ( A  u.  B
)  <->  Ord  A ) )
54biimprcd 216 . . 3  |-  ( Ord 
A  ->  ( ( A  u.  B )  =  A  ->  Ord  ( A  u.  B )
) )
6 ordeq 4399 . . . 4  |-  ( ( A  u.  B )  =  B  ->  ( Ord  ( A  u.  B
)  <->  Ord  B ) )
76biimprcd 216 . . 3  |-  ( Ord 
B  ->  ( ( A  u.  B )  =  B  ->  Ord  ( A  u.  B )
) )
85, 7jaao 495 . 2  |-  ( ( Ord  A  /\  Ord  B )  ->  ( (
( A  u.  B
)  =  A  \/  ( A  u.  B
)  =  B )  ->  Ord  ( A  u.  B ) ) )
93, 8mpd 14 1  |-  ( ( Ord  A  /\  Ord  B )  ->  Ord  ( A  u.  B ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    \/ wo 357    /\ wa 358    = wceq 1623    u. cun 3150   Ord word 4391
This theorem is referenced by:  ordsucun  4616  r0weon  7640
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1533  ax-5 1544  ax-17 1603  ax-9 1635  ax-8 1643  ax-14 1688  ax-6 1703  ax-7 1708  ax-11 1715  ax-12 1866  ax-ext 2264  ax-sep 4141  ax-nul 4149  ax-pr 4214
This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-3or 935  df-3an 936  df-tru 1310  df-ex 1529  df-nf 1532  df-sb 1630  df-eu 2147  df-mo 2148  df-clab 2270  df-cleq 2276  df-clel 2279  df-nfc 2408  df-ne 2448  df-ral 2548  df-rex 2549  df-rab 2552  df-v 2790  df-sbc 2992  df-dif 3155  df-un 3157  df-in 3159  df-ss 3166  df-pss 3168  df-nul 3456  df-if 3566  df-sn 3646  df-pr 3647  df-op 3649  df-uni 3828  df-br 4024  df-opab 4078  df-tr 4114  df-eprel 4305  df-po 4314  df-so 4315  df-fr 4352  df-we 4354  df-ord 4395
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