Theorem 1st0 8019

Description: The value of the first-member function at the empty set. (Contributed by NM, 23-Apr-2007.)

Assertion

Ref	Expression
1st0	⊢ (1st ‘∅) = ∅

Proof of Theorem 1st0

Step	Hyp	Ref	Expression
1		1stval 8015	. 2 ⊢ (1st ‘∅) = ∪ dom {∅}
2		dmsn0 6231	. . 3 ⊢ dom {∅} = ∅
3	2	unieqi 4924	. 2 ⊢ ∪ dom {∅} = ∪ ∅
4		uni0 4940	. 2 ⊢ ∪ ∅ = ∅
5	1, 3, 4	3eqtri 2767	1 ⊢ (1st ‘∅) = ∅

Syntax hints:   = wceq 1537  ∅c0 4339  {csn 4631  ∪ cuni 4912  dom cdm 5689  ‘cfv 6563  1^st c1st 8011

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1908  ax-6 1965  ax-7 2005  ax-8 2108  ax-9 2116  ax-10 2139  ax-11 2155  ax-12 2175  ax-ext 2706  ax-sep 5302  ax-nul 5312  ax-pr 5438  ax-un 7754

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-3an 1088  df-tru 1540  df-fal 1550  df-ex 1777  df-nf 1781  df-sb 2063  df-mo 2538  df-eu 2567  df-clab 2713  df-cleq 2727  df-clel 2814  df-nfc 2890  df-ne 2939  df-ral 3060  df-rex 3069  df-rab 3434  df-v 3480  df-dif 3966  df-un 3968  df-in 3970  df-ss 3980  df-nul 4340  df-if 4532  df-sn 4632  df-pr 4634  df-op 4638  df-uni 4913  df-br 5149  df-opab 5211  df-mpt 5232  df-id 5583  df-xp 5695  df-rel 5696  df-cnv 5697  df-co 5698  df-dm 5699  df-rn 5700  df-iota 6516  df-fun 6565  df-fv 6571  df-1st 8013

This theorem is referenced by:  vafval  30632