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Theorem unss1 3432
 Description: Subclass law for union of classes. (Contributed by NM, 14-Oct-1999.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)
Assertion
Ref Expression
unss1

Proof of Theorem unss1
Dummy variable is distinct from all other variables.
StepHypRef Expression
1 ssel 3267 . . . 4
21orim1d 812 . . 3
3 elun 3220 . . 3
4 elun 3220 . . 3
52, 3, 43imtr4g 261 . 2
65ssrdv 3278 1
 Colors of variables: wff setvar class Syntax hints:   wi 4   wo 357   wcel 1710   cun 3207   wss 3257 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334 This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2478  df-v 2861  df-nin 3211  df-compl 3212  df-in 3213  df-un 3214  df-ss 3259 This theorem is referenced by:  unss2  3434  unss12  3435  pwadjoin  4119
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