Theorem u1lem9ab 779

Description: Lemma used in study of orthoarguesian law.

Assertion

Ref	Expression
u1lem9ab	(a' ->1 b)' =< (a ->1 b)

Proof of Theorem u1lem9ab

Step	Hyp	Ref	Expression
1		u1lem9a 777	. 2 (a' ->1 b)' =< a'
2		u1lem9b 778	. 2 a' =< (a ->1 b)
3	1, 2	letr 137	1 (a' ->1 b)' =< (a ->1 b)

Syntax hints:   =< wle 2  'wn 4   ->1 wi1 12

This theorem is referenced by:  3vcom 813  oa3-u1 991  oa3-u2 992

This theorem was proved from axioms:  ax-a1 30  ax-a2 31  ax-a3 32  ax-a5 34  ax-r1 35  ax-r2 36  ax-r4 37  ax-r5 38

This theorem depends on definitions:  df-a 40  df-i1 44  df-le1 130  df-le2 131

Copyright terms: Public domain