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Theorem dfun3 3407
 Description: Union defined in terms of intersection (DeMorgan's law). Definition of union in [Mendelson] p. 231. (Contributed by NM, 8-Jan-2002.)
Assertion
Ref Expression
dfun3

Proof of Theorem dfun3
StepHypRef Expression
1 dfun2 3404 . 2
2 dfin2 3405 . . . 4
3 ddif 3308 . . . . 5
43difeq2i 3291 . . . 4
52, 4eqtr2i 2304 . . 3
65difeq2i 3291 . 2
71, 6eqtri 2303 1
 Colors of variables: wff set class Syntax hints:   wceq 1623  cvv 2788   cdif 3149   cun 3150   cin 3151 This theorem is referenced by:  difundi  3421  undifv  3528 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-6 1703  ax-7 1708  ax-11 1715  ax-12 1866  ax-ext 2264 This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-tru 1310  df-ex 1529  df-nf 1532  df-sb 1630  df-clab 2270  df-cleq 2276  df-clel 2279  df-nfc 2408  df-ral 2548  df-rab 2552  df-v 2790  df-dif 3155  df-un 3157  df-in 3159
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