Theorem bj-pr1val 37279

Description: Value of the first projection. (Contributed by BJ, 6-Apr-2019.)

Assertion

Ref	Expression
bj-pr1val	⊢ pr1 ({𝐴} × tag 𝐵) = if(𝐴 = ∅, 𝐵, ∅)

Proof of Theorem bj-pr1val

Step	Hyp	Ref	Expression
1		df-bj-pr1 37276	. 2 ⊢ pr1 ({𝐴} × tag 𝐵) = (∅ Proj ({𝐴} × tag 𝐵))
2		0ex 5256	. . 3 ⊢ ∅ ∈ V
3		bj-projval 37271	. . 3 ⊢ (∅ ∈ V → (∅ Proj ({𝐴} × tag 𝐵)) = if(𝐴 = ∅, 𝐵, ∅))
4	2, 3	ax-mp 5	. 2 ⊢ (∅ Proj ({𝐴} × tag 𝐵)) = if(𝐴 = ∅, 𝐵, ∅)
5	1, 4	eqtri 2760	1 ⊢ pr1 ({𝐴} × tag 𝐵) = if(𝐴 = ∅, 𝐵, ∅)

Syntax hints:   = wceq 1542   ∈ wcel 2114  Vcvv 3442  ∅c0 4287  ifcif 4481  {csn 4582   × cxp 5632  tag bj-ctag 37249   Proj bj-cproj 37265  pr₁ bj-cpr1 37275

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1969  ax-7 2010  ax-8 2116  ax-9 2124  ax-11 2163  ax-12 2185  ax-ext 2709  ax-sep 5245  ax-nul 5255  ax-pr 5381

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 849  df-3an 1089  df-tru 1545  df-fal 1555  df-ex 1782  df-sb 2069  df-clab 2716  df-cleq 2729  df-clel 2812  df-ne 2934  df-ral 3053  df-rex 3063  df-rab 3402  df-v 3444  df-dif 3906  df-un 3908  df-in 3910  df-ss 3920  df-nul 4288  df-if 4482  df-sn 4583  df-pr 4585  df-op 4589  df-br 5101  df-opab 5163  df-xp 5640  df-rel 5641  df-cnv 5642  df-dm 5644  df-rn 5645  df-res 5646  df-ima 5647  df-bj-sngl 37241  df-bj-tag 37250  df-bj-proj 37266  df-bj-pr1 37276

This theorem is referenced by:  bj-pr11val  37280  bj-pr21val  37288