Theorem pm1.5

Description: Axiom *1.5 (Assoc) of WhiteheadRussell p. 96. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm1.5	|- ( ( ph \/ ( ps \/ ch ) ) -> ( ps \/ ( ph \/ ch ) ) )

Proof

Step	Hyp	Ref	Expression
1		orc	|- ( ph -> ( ph \/ ch ) )
2	1	olcd	|- ( ph -> ( ps \/ ( ph \/ ch ) ) )
3		olc	|- ( ch -> ( ph \/ ch ) )
4	3	orim2i	|- ( ( ps \/ ch ) -> ( ps \/ ( ph \/ ch ) ) )
5	2 4	jaoi	|- ( ( ph \/ ( ps \/ ch ) ) -> ( ps \/ ( ph \/ ch ) ) )