Theorem ifbothdc 3564

Description: A wff 𝜃 containing a conditional operator is true when both of its cases are true. (Contributed by Jim Kingdon, 8-Aug-2021.)

Hypotheses

Ref	Expression
ifbothdc.1	⊢ (𝐴 = if(𝜑, 𝐴, 𝐵) → (𝜓 ↔ 𝜃))
ifbothdc.2	⊢ (𝐵 = if(𝜑, 𝐴, 𝐵) → (𝜒 ↔ 𝜃))

Assertion

Ref	Expression
ifbothdc	⊢ ((𝜓 ∧ 𝜒 ∧ DECID 𝜑) → 𝜃)

Proof of Theorem ifbothdc

Step	Hyp	Ref	Expression
1		iftrue 3537	. . . . . 6 ⊢ (𝜑 → if(𝜑, 𝐴, 𝐵) = 𝐴)
2	1	eqcomd 2181	. . . . 5 ⊢ (𝜑 → 𝐴 = if(𝜑, 𝐴, 𝐵))
3		ifbothdc.1	. . . . 5 ⊢ (𝐴 = if(𝜑, 𝐴, 𝐵) → (𝜓 ↔ 𝜃))
4	2, 3	syl 14	. . . 4 ⊢ (𝜑 → (𝜓 ↔ 𝜃))
5	4	biimpcd 159	. . 3 ⊢ (𝜓 → (𝜑 → 𝜃))
6	5	3ad2ant1 1018	. 2 ⊢ ((𝜓 ∧ 𝜒 ∧ DECID 𝜑) → (𝜑 → 𝜃))
7		iffalse 3540	. . . . . 6 ⊢ (¬ 𝜑 → if(𝜑, 𝐴, 𝐵) = 𝐵)
8	7	eqcomd 2181	. . . . 5 ⊢ (¬ 𝜑 → 𝐵 = if(𝜑, 𝐴, 𝐵))
9		ifbothdc.2	. . . . 5 ⊢ (𝐵 = if(𝜑, 𝐴, 𝐵) → (𝜒 ↔ 𝜃))
10	8, 9	syl 14	. . . 4 ⊢ (¬ 𝜑 → (𝜒 ↔ 𝜃))
11	10	biimpcd 159	. . 3 ⊢ (𝜒 → (¬ 𝜑 → 𝜃))
12	11	3ad2ant2 1019	. 2 ⊢ ((𝜓 ∧ 𝜒 ∧ DECID 𝜑) → (¬ 𝜑 → 𝜃))
13		exmiddc 836	. . 3 ⊢ (DECID 𝜑 → (𝜑 ∨ ¬ 𝜑))
14	13	3ad2ant3 1020	. 2 ⊢ ((𝜓 ∧ 𝜒 ∧ DECID 𝜑) → (𝜑 ∨ ¬ 𝜑))
15	6, 12, 14	mpjaod 718	1 ⊢ ((𝜓 ∧ 𝜒 ∧ DECID 𝜑) → 𝜃)

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 105   ∨ wo 708  DECID wdc 834   ∧ w3a 978   = wceq 1353  ifcif 3532

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in2 615  ax-io 709  ax-5 1445  ax-7 1446  ax-gen 1447  ax-ie1 1491  ax-ie2 1492  ax-8 1502  ax-11 1504  ax-4 1508  ax-17 1524  ax-i9 1528  ax-ial 1532  ax-i5r 1533  ax-ext 2157

This theorem depends on definitions:  df-bi 117  df-dc 835  df-3an 980  df-nf 1459  df-sb 1761  df-clab 2162  df-cleq 2168  df-clel 2171  df-if 3533

This theorem is referenced by:  isumlessdc  11470  pcmptdvds  12308