Theorem xorbi12iOLD

Description: Obsolete version of xorbi12i as of 21-Apr-2024. (Contributed by Mario Carneiro, 4-Sep-2016) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	xorbi12.1	|- ( ph <-> ps )
	xorbi12.2	|- ( ch <-> th )
Assertion	xorbi12iOLD	|- ( ( ph \/_ ch ) <-> ( ps \/_ th ) )

Proof

Step	Hyp	Ref	Expression
1		xorbi12.1	|- ( ph <-> ps )
2		xorbi12.2	|- ( ch <-> th )
3	1 2	bibi12i	|- ( ( ph <-> ch ) <-> ( ps <-> th ) )
4	3	notbii	|- ( -. ( ph <-> ch ) <-> -. ( ps <-> th ) )
5		df-xor	|- ( ( ph \/_ ch ) <-> -. ( ph <-> ch ) )
6		df-xor	|- ( ( ps \/_ th ) <-> -. ( ps <-> th ) )
7	4 5 6	3bitr4i	|- ( ( ph \/_ ch ) <-> ( ps \/_ th ) )