Theorem unisuc 4335

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 3246	. 2 |- ( U. A C_ A <-> ( U. A u. A ) = A )
2		df-tr 4027	. 2 |- ( Tr A <-> U. A C_ A )
3		df-suc 4293	. . . . 5 |- suc A = ( A u. { A } )
4	3	unieqi 3746	. . . 4 |- U. suc A = U. ( A u. { A } )
5		uniun 3755	. . . 4 |- U. ( A u. { A } ) = ( U. A u. U. { A } )
6		unisuc.1	. . . . . 6 |- A e. _V
7	6	unisn 3752	. . . . 5 |- U. { A } = A
8	7	uneq2i 3227	. . . 4 |- ( U. A u. U. { A } ) = ( U. A u. A )
9	4, 5, 8	3eqtri 2164	. . 3 |- U. suc A = ( U. A u. A )
10	9	eqeq1i 2147	. 2 |- ( U. suc A = A <-> ( U. A u. A ) = A )
11	1, 2, 10	3bitr4i 211	1 |- ( Tr A <-> U. suc A = A )

Syntax hints:   <-> wb 104   = wceq 1331   e. wcel 1480   _Vcvv 2686   u. cun 3069   C_ wss 3071   {csn 3527   U.cuni 3736   Tr wtr 4026   suc csuc 4287

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 698  ax-5 1423  ax-7 1424  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-8 1482  ax-10 1483  ax-11 1484  ax-i12 1485  ax-bndl 1486  ax-4 1487  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2121

This theorem depends on definitions:  df-bi 116  df-tru 1334  df-nf 1437  df-sb 1736  df-clab 2126  df-cleq 2132  df-clel 2135  df-nfc 2270  df-rex 2422  df-v 2688  df-un 3075  df-in 3077  df-ss 3084  df-sn 3533  df-pr 3534  df-uni 3737  df-tr 4027  df-suc 4293

This theorem is referenced by:  onunisuci  4354  ordsucunielexmid  4446  tfrexlem  6231  nnsucuniel  6391