Theorem ifr0 42027

Description: A class that is founded by the identity relation is null. (Contributed by Andrew Salmon, 25-Jul-2011.)

Assertion

Ref	Expression
ifr0	⊢ ( I Fr 𝐴 ↔ 𝐴 = ∅)

Proof of Theorem ifr0

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		equid 2015	. . . . 5 ⊢ 𝑥 = 𝑥
2		vex 3434	. . . . . 6 ⊢ 𝑥 ∈ V
3	2	ideq 5755	. . . . 5 ⊢ (𝑥 I 𝑥 ↔ 𝑥 = 𝑥)
4	1, 3	mpbir 230	. . . 4 ⊢ 𝑥 I 𝑥
5		frirr 5562	. . . . 5 ⊢ (( I Fr 𝐴 ∧ 𝑥 ∈ 𝐴) → ¬ 𝑥 I 𝑥)
6	5	ex 413	. . . 4 ⊢ ( I Fr 𝐴 → (𝑥 ∈ 𝐴 → ¬ 𝑥 I 𝑥))
7	4, 6	mt2i 137	. . 3 ⊢ ( I Fr 𝐴 → ¬ 𝑥 ∈ 𝐴)
8	7	eq0rdv 4339	. 2 ⊢ ( I Fr 𝐴 → 𝐴 = ∅)
9		fr0 5564	. . 3 ⊢ I Fr ∅
10		freq2 5556	. . 3 ⊢ (𝐴 = ∅ → ( I Fr 𝐴 ↔ I Fr ∅))
11	9, 10	mpbiri 257	. 2 ⊢ (𝐴 = ∅ → I Fr 𝐴)
12	8, 11	impbii 208	1 ⊢ ( I Fr 𝐴 ↔ 𝐴 = ∅)

Syntax hints:  ¬ wn 3   ↔ wb 205   = wceq 1539   ∈ wcel 2106  ∅c0 4257   class class class wbr 5074   I cid 5484   Fr wfr 5537

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1798  ax-4 1812  ax-5 1913  ax-6 1971  ax-7 2011  ax-8 2108  ax-9 2116  ax-ext 2709  ax-sep 5222  ax-nul 5229  ax-pr 5351

This theorem depends on definitions:  df-bi 206  df-an 397  df-or 845  df-3an 1088  df-tru 1542  df-fal 1552  df-ex 1783  df-sb 2068  df-clab 2716  df-cleq 2730  df-clel 2816  df-ne 2944  df-ral 3069  df-rex 3070  df-rab 3073  df-v 3432  df-dif 3890  df-un 3892  df-in 3894  df-ss 3904  df-nul 4258  df-if 4461  df-pw 4536  df-sn 4563  df-pr 4565  df-op 4569  df-br 5075  df-opab 5137  df-id 5485  df-fr 5540  df-xp 5591  df-rel 5592

This theorem is referenced by: (None)