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Theorem npss 3425
Description: A class is not a proper subclass of another iff it satisfies a one-directional form of eqss 3331. (Contributed by Mario Carneiro, 15-May-2015.)
Assertion
Ref Expression
npss  |-  ( -.  A  C.  B  <->  ( A  C_  B  ->  A  =  B ) )

Proof of Theorem npss
StepHypRef Expression
1 pm4.61 416 . . 3  |-  ( -.  ( A  C_  B  ->  A  =  B )  <-> 
( A  C_  B  /\  -.  A  =  B ) )
2 dfpss2 3400 . . 3  |-  ( A 
C.  B  <->  ( A  C_  B  /\  -.  A  =  B ) )
31, 2bitr4i 244 . 2  |-  ( -.  ( A  C_  B  ->  A  =  B )  <-> 
A  C.  B )
43con1bii 322 1  |-  ( -.  A  C.  B  <->  ( A  C_  B  ->  A  =  B ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 177    /\ wa 359    = wceq 1649    C_ wss 3288    C. wpss 3289
This theorem is referenced by:  ttukeylem7  8359  canthp1lem2  8492  pgpfac1lem1  15595  lspsncv0  16181  obslbs  16920
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
This theorem depends on definitions:  df-bi 178  df-an 361  df-ne 2577  df-pss 3304
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