Theorem cnfn1dd

Description: A lemma for Conjunctive Normal Form unit propagation, in double deduction form. (Contributed by Giovanni Mascellani, 19-Mar-2018)

	Ref	Expression
Hypotheses	cnfn1dd.1	|- ( ph -> ( ps -> ch ) )
	cnfn1dd.2	|- ( ph -> ( ps -> ( -. ch \/ th ) ) )
Assertion	cnfn1dd	|- ( ph -> ( ps -> th ) )

Proof

Step	Hyp	Ref	Expression
1		cnfn1dd.1	|- ( ph -> ( ps -> ch ) )
2		cnfn1dd.2	|- ( ph -> ( ps -> ( -. ch \/ th ) ) )
3		notnot	|- ( ch -> -. -. ch )
4	1 3	syl6	|- ( ph -> ( ps -> -. -. ch ) )
5	4 2	cnf1dd	|- ( ph -> ( ps -> th ) )