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Theorem iffalse 3482
 Description: Value of the conditional operator when its first argument is false. (Contributed by NM, 14-Aug-1999.)
Assertion
Ref Expression
iffalse 𝜑 → if(𝜑, 𝐴, 𝐵) = 𝐵)

Proof of Theorem iffalse
Dummy variable 𝑥 is distinct from all other variables.
StepHypRef Expression
1 dedlemb 954 . . 3 𝜑 → (𝑥𝐵 ↔ ((𝑥𝐴𝜑) ∨ (𝑥𝐵 ∧ ¬ 𝜑))))
21abbi2dv 2258 . 2 𝜑𝐵 = {𝑥 ∣ ((𝑥𝐴𝜑) ∨ (𝑥𝐵 ∧ ¬ 𝜑))})
3 df-if 3475 . 2 if(𝜑, 𝐴, 𝐵) = {𝑥 ∣ ((𝑥𝐴𝜑) ∨ (𝑥𝐵 ∧ ¬ 𝜑))}
42, 3syl6reqr 2191 1 𝜑 → if(𝜑, 𝐴, 𝐵) = 𝐵)
 Colors of variables: wff set class Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 103   ∨ wo 697   = wceq 1331   ∈ wcel 1480  {cab 2125  ifcif 3474 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in2 604  ax-io 698  ax-5 1423  ax-7 1424  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-8 1482  ax-11 1484  ax-4 1487  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2121 This theorem depends on definitions:  df-bi 116  df-nf 1437  df-sb 1736  df-clab 2126  df-cleq 2132  df-clel 2135  df-if 3475 This theorem is referenced by:  iffalsei  3483  iffalsed  3484  ifnefalse  3485  ifsbdc  3486  ifcldadc  3501  ifeq1dadc  3502  ifbothdadc  3503  ifbothdc  3504  ifiddc  3505  ifcldcd  3507  ifandc  3508  fidifsnen  6764  nnnninf  7023  uzin  9370  modifeq2int  10171  bcval  10507  bcval3  10509  sumrbdclem  11158  fsum3cvg  11159  summodclem2a  11162  sumsplitdc  11213  prodrbdclem  11352  fproddccvg  11353  flodddiv4  11642  gcdn0val  11661  dfgcd2  11713  lcmn0val  11758  unct  11966
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