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	⊢ ¬ 𝐴 ⊊ 𝐴

Proof

Step	Hyp	Ref	Expression
1		pm3.24	⊢ ¬ ( 𝐴 ⊆ 𝐴 ∧ ¬ 𝐴 ⊆ 𝐴 )
2		dfpss3	⊢ ( 𝐴 ⊊ 𝐴 ↔ ( 𝐴 ⊆ 𝐴 ∧ ¬ 𝐴 ⊆ 𝐴 ) )
3	1 2	mtbir	⊢ ¬ 𝐴 ⊊ 𝐴