Theorem oibabs 881

Description: Absorption of disjunction into equivalence. (Contributed by NM, 6-Aug-1995.) (Proof shortened by Wolf Lammen, 3-Nov-2013.)

Assertion

Ref	Expression
oibabs

Proof of Theorem oibabs

Step	Hyp	Ref	Expression
1		norbi 859	. . 3
2		id 22	. . 3
3	1, 2	ja 161	. 2
4		ax-1 6	. 2
5	3, 4	impbii 188	1

Syntax hints:  ->wi 4  <->wb 184  \/wo 368

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

This theorem depends on definitions:  df-bi 185  df-or 370