Theorem dfif2 4467

Description: An alternate definition of the conditional operator df-if 4466 with one fewer connectives (but probably less intuitive to understand). (Contributed by NM, 30-Jan-2006.)

Assertion

Ref	Expression
dfif2	⊢ if(𝜑, 𝐴, 𝐵) = {𝑥 ∣ ((𝑥 ∈ 𝐵 → 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑))}

Distinct variable groups:   𝜑,𝑥   𝑥,𝐴   𝑥,𝐵

Proof of Theorem dfif2

Step	Hyp	Ref	Expression
1		df-if 4466	. 2 ⊢ if(𝜑, 𝐴, 𝐵) = {𝑥 ∣ ((𝑥 ∈ 𝐴 ∧ 𝜑) ∨ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑))}
2		df-or 846	. . . 4 ⊢ (((𝑥 ∈ 𝐵 ∧ ¬ 𝜑) ∨ (𝑥 ∈ 𝐴 ∧ 𝜑)) ↔ (¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑)))
3		orcom 868	. . . 4 ⊢ (((𝑥 ∈ 𝐴 ∧ 𝜑) ∨ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑)) ↔ ((𝑥 ∈ 𝐵 ∧ ¬ 𝜑) ∨ (𝑥 ∈ 𝐴 ∧ 𝜑)))
4		iman 403	. . . . 5 ⊢ ((𝑥 ∈ 𝐵 → 𝜑) ↔ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑))
5	4	imbi1i 350	. . . 4 ⊢ (((𝑥 ∈ 𝐵 → 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑)) ↔ (¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑)))
6	2, 3, 5	3bitr4i 303	. . 3 ⊢ (((𝑥 ∈ 𝐴 ∧ 𝜑) ∨ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑)) ↔ ((𝑥 ∈ 𝐵 → 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑)))
7	6	abbii 2806	. 2 ⊢ {𝑥 ∣ ((𝑥 ∈ 𝐴 ∧ 𝜑) ∨ (𝑥 ∈ 𝐵 ∧ ¬ 𝜑))} = {𝑥 ∣ ((𝑥 ∈ 𝐵 → 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑))}
8	1, 7	eqtri 2764	1 ⊢ if(𝜑, 𝐴, 𝐵) = {𝑥 ∣ ((𝑥 ∈ 𝐵 → 𝜑) → (𝑥 ∈ 𝐴 ∧ 𝜑))}

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 397   ∨ wo 845   = wceq 1539   ∈ wcel 2104  {cab 2713  ifcif 4465

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1911  ax-6 1969  ax-7 2009  ax-9 2114  ax-ext 2707

This theorem depends on definitions:  df-bi 206  df-an 398  df-or 846  df-ex 1780  df-sb 2066  df-clab 2714  df-cleq 2728  df-if 4466

This theorem is referenced by:  iftrue  4471  nfifd  4494