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Theorem pssss 3033
Description: A proper subclass is a subclass. Theorem 10 of [Suppes] p. 23. (Contributed by NM, 7-Feb-1996.)
Assertion
Ref Expression
pssss (ABAB)

Proof of Theorem pssss
StepHypRef Expression
1 df-pss 2927 . 2 (AB ↔ (AB AB))
21simplbi 259 1 (ABAB)
Colors of variables: wff set class
Syntax hints:  wi 4  wne 2201  wss 2911  wpss 2912
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 2927
This theorem is referenced by:  pssssd  3035  sspssr  3037  pssn2lp  3039  sspsstrir  3040  psstr  3043  sspsstr  3044  psssstr  3045
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