Theorem pssirrOLD

Description: Obsolete version of pssirr as of 10-Jun-2026. (Contributed by NM, 7-Feb-1996) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	pssirrOLD	$$⊢\neg A\subset A$$

Proof

Step	Hyp	Ref	Expression
1		pm3.24	$$⊢\neg \left(A\subseteq A\wedge \neg A\subseteq A\right)$$
2		dfpss3	$$⊢A\subset A\leftrightarrow \left(A\subseteq A\wedge \neg A\subseteq A\right)$$
3	1 2	mtbir	$$⊢\neg A\subset A$$