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Theorem ifeq1 3912
Description: Equality theorem for conditional operator. (Contributed by NM, 1-Sep-2004.) (Revised by Mario Carneiro, 8-Sep-2013.)
Assertion
Ref Expression
ifeq1 (𝐴 = 𝐵 → if(𝜑, 𝐴, 𝐶) = if(𝜑, 𝐵, 𝐶))

Proof of Theorem ifeq1
Dummy variable 𝑥 is distinct from all other variables.
StepHypRef Expression
1 rabeq 3059 . . 3 (𝐴 = 𝐵 → {𝑥𝐴𝜑} = {𝑥𝐵𝜑})
21uneq1d 3614 . 2 (𝐴 = 𝐵 → ({𝑥𝐴𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑}) = ({𝑥𝐵𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑}))
3 dfif6 3911 . 2 if(𝜑, 𝐴, 𝐶) = ({𝑥𝐴𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑})
4 dfif6 3911 . 2 if(𝜑, 𝐵, 𝐶) = ({𝑥𝐵𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑})
52, 3, 43eqtr4g 2564 1 (𝐴 = 𝐵 → if(𝜑, 𝐴, 𝐶) = if(𝜑, 𝐵, 𝐶))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4   = wceq 1468  {crab 2795  cun 3424  ifcif 3908
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1698  ax-4 1711  ax-5 1789  ax-6 1836  ax-7 1883  ax-10 1965  ax-11 1970  ax-12 1983  ax-13 2137  ax-ext 2485
This theorem depends on definitions:  df-bi 192  df-or 379  df-an 380  df-tru 1471  df-ex 1693  df-nf 1697  df-sb 1829  df-clab 2492  df-cleq 2498  df-clel 2501  df-nfc 2635  df-rab 2800  df-v 3068  df-un 3431  df-if 3909
This theorem is referenced by:  ifeq12  3925  ifeq1d  3926  ifbieq12i  3934  ifexg  3977  rdgeq2  7207  dfoi  8109  wemaplem2  8145  cantnflem1  8279  prodeq2w  14126  prodeq2ii  14127  mgm2nsgrplem2  16813  mgm2nsgrplem3  16814  mplcoe3  18849  marrepval0  19744  ellimc  22989  ply1nzb  23232  dchrvmasumiflem1  24500  signspval  29594  dfrdg2  30593  dfafv2  39154
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