Theorem 2false

Description: Two falsehoods are equivalent. (Contributed by NM, 4-Apr-2005) (Proof shortened by Wolf Lammen, 19-May-2013)

	Ref	Expression
Hypotheses	2false.1	|- -. ph
	2false.2	|- -. ps
Assertion	2false	|- ( ph <-> ps )

Proof

Step	Hyp	Ref	Expression
1		2false.1	|- -. ph
2		2false.2	|- -. ps
3	1 2	2th	|- ( -. ph <-> -. ps )
4	3	con4bii	|- ( ph <-> ps )