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Theorem ifeq1 4039
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 3165 . . 3 (𝐴 = 𝐵 → {𝑥𝐴𝜑} = {𝑥𝐵𝜑})
21uneq1d 3727 . 2 (𝐴 = 𝐵 → ({𝑥𝐴𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑}) = ({𝑥𝐵𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑}))
3 dfif6 4038 . 2 if(𝜑, 𝐴, 𝐶) = ({𝑥𝐴𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑})
4 dfif6 4038 . 2 if(𝜑, 𝐵, 𝐶) = ({𝑥𝐵𝜑} ∪ {𝑥𝐶 ∣ ¬ 𝜑})
52, 3, 43eqtr4g 2668 1 (𝐴 = 𝐵 → if(𝜑, 𝐴, 𝐶) = if(𝜑, 𝐵, 𝐶))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4   = wceq 1474  {crab 2899  cun 3537  ifcif 4035
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1712  ax-4 1727  ax-5 1826  ax-6 1874  ax-7 1921  ax-10 2005  ax-11 2020  ax-12 2032  ax-13 2232  ax-ext 2589
This theorem depends on definitions:  df-bi 195  df-or 383  df-an 384  df-tru 1477  df-ex 1695  df-nf 1700  df-sb 1867  df-clab 2596  df-cleq 2602  df-clel 2605  df-nfc 2739  df-rab 2904  df-v 3174  df-un 3544  df-if 4036
This theorem is referenced by:  ifeq12  4052  ifeq1d  4053  ifbieq12i  4061  ifexg  4106  rdgeq2  7372  dfoi  8276  wemaplem2  8312  cantnflem1  8446  prodeq2w  14427  prodeq2ii  14428  mgm2nsgrplem2  17175  mgm2nsgrplem3  17176  mplcoe3  19233  marrepval0  20128  ellimc  23360  ply1nzb  23603  dchrvmasumiflem1  24907  signspval  29761  dfrdg2  30751  dfafv2  39666
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