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Theorem pssss 3364
Description: A proper subclass is a subclass. Theorem 10 of [Suppes] p. 23. (Contributed by NM, 7-Feb-1996.)
Assertion
Ref Expression
pssss (ABA B)

Proof of Theorem pssss
StepHypRef Expression
1 df-pss 3261 . 2 (AB ↔ (A B AB))
21simplbi 446 1 (ABA B)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wne 2516   wss 3257  wpss 3258
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 177  df-an 360  df-pss 3261
This theorem is referenced by:  pssssd  3366  sspss  3368  pssn2lp  3370  psstr  3373
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