Theorem xorneg

Description: The connector \/_ is unchanged under negation of both arguments. (Contributed by Mario Carneiro, 4-Sep-2016)

	Ref	Expression
Assertion	xorneg	|- ( ( -. ph \/_ -. ps ) <-> ( ph \/_ ps ) )

Proof

Step	Hyp	Ref	Expression
1		xorneg1	|- ( ( -. ph \/_ -. ps ) <-> -. ( ph \/_ -. ps ) )
2		xorneg2	|- ( ( ph \/_ -. ps ) <-> -. ( ph \/_ ps ) )
3	2	con2bii	|- ( ( ph \/_ ps ) <-> -. ( ph \/_ -. ps ) )
4	1 3	bitr4i	|- ( ( -. ph \/_ -. ps ) <-> ( ph \/_ ps ) )