Theorem unisuc 4539

Description: A transitive class is equal to the union of its successor. Combines Theorem 4E of [Enderton] p. 72 and Exercise 6 of [Enderton] p. 73. (Contributed by NM, 30-Aug-1993.)

Hypothesis

Ref	Expression
unisuc.1	|- A e. _V

Assertion

Ref	Expression
unisuc	|- ( Tr A <-> U. suc A = A )

Proof of Theorem unisuc

Step	Hyp	Ref	Expression
1		ssequn1 3393	. 2 |- ( U. A C_ A <-> ( U. A u. A ) = A )
2		df-tr 4214	. 2 |- ( Tr A <-> U. A C_ A )
3		df-suc 4497	. . . . 5 |- suc A = ( A u. { A } )
4	3	unieqi 3929	. . . 4 |- U. suc A = U. ( A u. { A } )
5		uniun 3938	. . . 4 |- U. ( A u. { A } ) = ( U. A u. U. { A } )
6		unisuc.1	. . . . . 6 |- A e. _V
7	6	unisn 3935	. . . . 5 |- U. { A } = A
8	7	uneq2i 3374	. . . 4 |- ( U. A u. U. { A } ) = ( U. A u. A )
9	4, 5, 8	3eqtri 2259	. . 3 |- U. suc A = ( U. A u. A )
10	9	eqeq1i 2242	. 2 |- ( U. suc A = A <-> ( U. A u. A ) = A )
11	1, 2, 10	3bitr4i 212	1 |- ( Tr A <-> U. suc A = A )

Syntax hints:   <-> wb 105   = wceq 1398   e. wcel 2205   _Vcvv 2815   u. cun 3212   C_ wss 3214   {csn 3694   U.cuni 3919   Tr wtr 4213   suc csuc 4491

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 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-ext 2216

This theorem depends on definitions:  df-bi 117  df-tru 1401  df-nf 1510  df-sb 1812  df-clab 2221  df-cleq 2227  df-clel 2230  df-nfc 2375  df-rex 2528  df-v 2817  df-un 3218  df-in 3220  df-ss 3227  df-sn 3700  df-pr 3701  df-uni 3920  df-tr 4214  df-suc 4497

This theorem is referenced by:  onunisuci  4558  ordsucunielexmid  4658  tfrexlem  6578  nnsucuniel  6741