Theorem imimorb 877

Description: Simplify an implication between implications. (Contributed by Paul Chapman, 17-Nov-2012.) (Proof shortened by Wolf Lammen, 3-Apr-2013.)

Assertion

Ref	Expression
imimorb

Proof of Theorem imimorb

Step	Hyp	Ref	Expression
1		bi2.04 361	. 2
2		dfor2 411	. . 3
3	2	imbi2i 312	. 2
4	1, 3	bitr4i 252	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