Theorem pssss 3039

Description: A proper subclass is a subclass. Theorem 10 of [Suppes] p. 23. (Contributed by NM, 7-Feb-1996.)

Assertion

Ref	Expression
pssss	⊢ (𝐴 ⊊ 𝐵 → 𝐴 ⊆ 𝐵)

Proof of Theorem pssss

Step	Hyp	Ref	Expression
1		df-pss 2933	. 2 ⊢ (𝐴 ⊊ 𝐵 ↔ (𝐴 ⊆ 𝐵 ∧ 𝐴 ≠ 𝐵))
2	1	simplbi 259	1 ⊢ (𝐴 ⊊ 𝐵 → 𝐴 ⊆ 𝐵)

Syntax hints:   → wi 4   ≠ wne 2204   ⊆ wss 2917   ⊊ wpss 2918

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99

This theorem depends on definitions:  df-bi 110  df-pss 2933

This theorem is referenced by:  pssssd  3041  sspssr  3043  pssn2lp  3045  sspsstrir  3046  psstr  3049  sspsstr  3050  psssstr  3051