Theorem pssssd

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

	Ref	Expression
Hypothesis	pssssd.1	$$⊢\phi \to A\subset B$$
Assertion	pssssd	$$⊢\phi \to A\subseteq B$$

Proof

Step	Hyp	Ref	Expression
1		pssssd.1	$$⊢\phi \to A\subset B$$
2		pssss	$$⊢A\subset B\to A\subseteq B$$
3	1 2	syl	$$⊢\phi \to A\subseteq B$$