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Theorem pssss 3016
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 2910 . 2 (AB ↔ (AB AB))
21simplbi 259 1 (ABAB)
Colors of variables: wff set class
Syntax hints:  wi 4  wne 2186  wss 2894  wpss 2895
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 2910
This theorem is referenced by:  pssssd  3018  sspssr  3020  pssn2lp  3022  sspsstrir  3023  psstr  3026  sspsstr  3027  psssstr  3028
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