Theorem pssssd

Description: Deduce subclass from proper subclass. (Contributed by NM, 29-Feb-1996)

	Ref	Expression
Hypothesis	pssssd.1	|- ( ph -> A C. B )
Assertion	pssssd	|- ( ph -> A C_ B )

Proof

Step	Hyp	Ref	Expression
1		pssssd.1	|- ( ph -> A C. B )
2		pssss	|- ( A C. B -> A C_ B )
3	1 2	syl	|- ( ph -> A C_ B )