Theorem 3anass

Description: Associative law for triple conjunction. (Contributed by NM, 8-Apr-1994)

	Ref	Expression
Assertion	3anass	|- ( ( ph /\ ps /\ ch ) <-> ( ph /\ ( ps /\ ch ) ) )

Proof

Step	Hyp	Ref	Expression
1		df-3an	|- ( ( ph /\ ps /\ ch ) <-> ( ( ph /\ ps ) /\ ch ) )
2		anass	|- ( ( ( ph /\ ps ) /\ ch ) <-> ( ph /\ ( ps /\ ch ) ) )
3	1 2	bitri	|- ( ( ph /\ ps /\ ch ) <-> ( ph /\ ( ps /\ ch ) ) )