Theorem dftr2 4190

Description: An alternate way of defining a transitive class. Exercise 7 of [TakeutiZaring] p. 40. (Contributed by NM, 24-Apr-1994.)

Assertion

Ref	Expression
dftr2	⊢ (Tr 𝐴 ↔ ∀𝑥∀𝑦((𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴))

Distinct variable group:   𝑥,𝑦,𝐴

Proof of Theorem dftr2

Step	Hyp	Ref	Expression
1		ssalel 3214	. 2 ⊢ (∪ 𝐴 ⊆ 𝐴 ↔ ∀𝑥(𝑥 ∈ ∪ 𝐴 → 𝑥 ∈ 𝐴))
2		df-tr 4189	. 2 ⊢ (Tr 𝐴 ↔ ∪ 𝐴 ⊆ 𝐴)
3		19.23v 1930	. . . 4 ⊢ (∀𝑦((𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴) ↔ (∃𝑦(𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴))
4		eluni 3897	. . . . 5 ⊢ (𝑥 ∈ ∪ 𝐴 ↔ ∃𝑦(𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴))
5	4	imbi1i 238	. . . 4 ⊢ ((𝑥 ∈ ∪ 𝐴 → 𝑥 ∈ 𝐴) ↔ (∃𝑦(𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴))
6	3, 5	bitr4i 187	. . 3 ⊢ (∀𝑦((𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴) ↔ (𝑥 ∈ ∪ 𝐴 → 𝑥 ∈ 𝐴))
7	6	albii 1518	. 2 ⊢ (∀𝑥∀𝑦((𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴) ↔ ∀𝑥(𝑥 ∈ ∪ 𝐴 → 𝑥 ∈ 𝐴))
8	1, 2, 7	3bitr4i 212	1 ⊢ (Tr 𝐴 ↔ ∀𝑥∀𝑦((𝑥 ∈ 𝑦 ∧ 𝑦 ∈ 𝐴) → 𝑥 ∈ 𝐴))

Syntax hints:   → wi 4   ∧ wa 104   ↔ wb 105  ∀wal 1395  ∃wex 1540   ∈ wcel 2201   ⊆ wss 3199  ∪ cuni 3894  Tr wtr 4188

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-io 716  ax-5 1495  ax-7 1496  ax-gen 1497  ax-ie1 1541  ax-ie2 1542  ax-8 1552  ax-10 1553  ax-11 1554  ax-i12 1555  ax-bndl 1557  ax-4 1558  ax-17 1574  ax-i9 1578  ax-ial 1582  ax-i5r 1583  ax-ext 2212

This theorem depends on definitions:  df-bi 117  df-tru 1400  df-nf 1509  df-sb 1810  df-clab 2217  df-cleq 2223  df-clel 2226  df-nfc 2362  df-v 2803  df-in 3205  df-ss 3212  df-uni 3895  df-tr 4189

This theorem is referenced by:  dftr5  4191  trel  4195  suctr  4520  ordtriexmidlem  4619  ordtri2or2exmidlem  4626  onsucelsucexmidlem  4629  ordsuc  4663  tfi  4682  ordom  4707