Theorem ka4ot 421

Description: 3-variable version of weakly orthomodular law. It is proved from a weaker-looking equivalent, wom2 420, which in turn is proved from ax-wom 347.

Assertion

Ref	Expression
ka4ot	((a == b)' v ((a v c) == (b v c))) = 1

Proof of Theorem ka4ot

Step	Hyp	Ref	Expression
1		le1 140	. 2 ((a == b)' v ((a v c) == (b v c))) =< 1
2		wom2 420	. . . . . 6 a =< ((a == b)' v ((a v c) == (b v c)))
3		wom2 420	. . . . . . 7 b =< ((b == a)' v ((b v c) == (a v c)))
4		bicom 90	. . . . . . . . 9 (b == a) = (a == b)
5	4	ax-r4 37	. . . . . . . 8 (b == a)' = (a == b)'
6		bicom 90	. . . . . . . 8 ((b v c) == (a v c)) = ((a v c) == (b v c))
7	5, 6	2or 68	. . . . . . 7 ((b == a)' v ((b v c) == (a v c))) = ((a == b)' v ((a v c) == (b v c)))
8	3, 7	lbtr 133	. . . . . 6 b =< ((a == b)' v ((a v c) == (b v c)))
9	2, 8	le2or 162	. . . . 5 (a v b) =< (((a == b)' v ((a v c) == (b v c))) v ((a == b)' v ((a v c) == (b v c))))
10		oridm 104	. . . . 5 (((a == b)' v ((a v c) == (b v c))) v ((a == b)' v ((a v c) == (b v c)))) = ((a == b)' v ((a v c) == (b v c)))
11	9, 10	lbtr 133	. . . 4 (a v b) =< ((a == b)' v ((a v c) == (b v c)))
12	11	leror 146	. . 3 ((a v b) v ((a v c) == (b v c))) =< (((a == b)' v ((a v c) == (b v c))) v ((a v c) == (b v c)))
13		ka4lemo 222	. . 3 ((a v b) v ((a v c) == (b v c))) = 1
14		ax-a3 32	. . . 4 (((a == b)' v ((a v c) == (b v c))) v ((a v c) == (b v c))) = ((a == b)' v (((a v c) == (b v c)) v ((a v c) == (b v c))))
15		oridm 104	. . . . 5 (((a v c) == (b v c)) v ((a v c) == (b v c))) = ((a v c) == (b v c))
16	15	lor 67	. . . 4 ((a == b)' v (((a v c) == (b v c)) v ((a v c) == (b v c)))) = ((a == b)' v ((a v c) == (b v c)))
17	14, 16	ax-r2 36	. . 3 (((a == b)' v ((a v c) == (b v c))) v ((a v c) == (b v c))) = ((a == b)' v ((a v c) == (b v c)))
18	12, 13, 17	le3tr2 135	. 2 1 =< ((a == b)' v ((a v c) == (b v c)))
19	1, 18	lebi 139	1 ((a == b)' v ((a v c) == (b v c))) = 1

Syntax hints:   = wb 1  'wn 4   == tb 5   v wo 6  1wt 8

This theorem is referenced by:  i3or 483

This theorem was proved from axioms:  ax-a1 30  ax-a2 31  ax-a3 32  ax-a4 33  ax-a5 34  ax-r1 35  ax-r2 36  ax-r4 37  ax-r5 38  ax-wom 347

This theorem depends on definitions:  df-b 39  df-a 40  df-t 41  df-f 42  df-i1 44  df-i2 45  df-le 123  df-le1 124  df-le2 125  df-cmtr 128

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