Theorem orbi1i 506

Description: Inference adding a right disjunct to both sides of a logical equivalence. (Contributed by NM, 5-Aug-1993.)

Hypothesis

Ref	Expression
orbi2i.1	|- (ph <-> ps)

Assertion

Ref	Expression
orbi1i	|- ((ph \/ ch) <-> (ps \/ ch))

Proof of Theorem orbi1i

Step	Hyp	Ref	Expression
1		orcom 376	. 2 |- ((ph \/ ch) <-> (ch \/ ph))
2		orbi2i.1	. . 3 |- (ph <-> ps)
3	2	orbi2i 505	. 2 |- ((ch \/ ph) <-> (ch \/ ps))
4		orcom 376	. 2 |- ((ch \/ ps) <-> (ps \/ ch))
5	1, 3, 4	3bitri 262	1 |- ((ph \/ ch) <-> (ps \/ ch))

Syntax hints:   <-> wb 176   \/ wo 357

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8

This theorem depends on definitions:  df-bi 177  df-or 359

This theorem is referenced by:  orbi12i  507  orordi  516  3anor  948  3or6  1263  19.45  1878  unass  3420  dfimak2  4298  ssfin  4470  eqtfinrelk  4486  evenoddnnnul  4514  nmembers1lem3  6270  nncdiv3  6277  nchoicelem6  6294  nchoicelem9  6297  nchoicelem18  6306