Theorem ersymb 6759

Description: An equivalence relation is symmetric. (Contributed by NM, 30-Jul-1995.) (Revised by Mario Carneiro, 12-Aug-2015.)

Hypothesis

Ref	Expression
ersymb.1	|- ( ph -> R Er X )

Assertion

Ref	Expression
ersymb	|- ( ph -> ( A R B <-> B R A ) )

Proof of Theorem ersymb

Step	Hyp	Ref	Expression
1		ersymb.1	. . . 4 |- ( ph -> R Er X )
2	1	adantr 276	. . 3 |- ( ( ph /\ A R B ) -> R Er X )
3		simpr 110	. . 3 |- ( ( ph /\ A R B ) -> A R B )
4	2, 3	ersym 6757	. 2 |- ( ( ph /\ A R B ) -> B R A )
5	1	adantr 276	. . 3 |- ( ( ph /\ B R A ) -> R Er X )
6		simpr 110	. . 3 |- ( ( ph /\ B R A ) -> B R A )
7	5, 6	ersym 6757	. 2 |- ( ( ph /\ B R A ) -> A R B )
8	4, 7	impbida 600	1 |- ( ph -> ( A R B <-> B R A ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   class class class wbr 4093   Er wer 6742

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-14 2205  ax-ext 2213  ax-sep 4212  ax-pow 4270  ax-pr 4305

This theorem depends on definitions:  df-bi 117  df-3an 1007  df-tru 1401  df-nf 1510  df-sb 1811  df-eu 2082  df-mo 2083  df-clab 2218  df-cleq 2224  df-clel 2227  df-nfc 2364  df-ral 2516  df-rex 2517  df-v 2805  df-un 3205  df-in 3207  df-ss 3214  df-pw 3658  df-sn 3679  df-pr 3680  df-op 3682  df-br 4094  df-opab 4156  df-xp 4737  df-rel 4738  df-cnv 4739  df-er 6745

This theorem is referenced by:  ercnv  6766  erth  6791  erth2  6792  iinerm  6819  ensymb  6997