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Theorem inf2 7513
Description: Variation of Axiom of Infinity. There exists a non-empty set that is a subset of its union (using zfinf 7529 as a hypothesis). Abbreviated version of the Axiom of Infinity in [FreydScedrov] p. 283. (Contributed by NM, 28-Oct-1996.)
Hypothesis
Ref Expression
inf1.1  |-  E. x
( y  e.  x  /\  A. y ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
Assertion
Ref Expression
inf2  |-  E. x
( x  =/=  (/)  /\  x  C_ 
U. x )
Distinct variable group:    x, y, z

Proof of Theorem inf2
StepHypRef Expression
1 inf1.1 . . 3  |-  E. x
( y  e.  x  /\  A. y ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
21inf1 7512 . 2  |-  E. x
( x  =/=  (/)  /\  A. y ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
3 dfss2 3282 . . . . 5  |-  ( x 
C_  U. x  <->  A. y
( y  e.  x  ->  y  e.  U. x
) )
4 eluni 3962 . . . . . . 7  |-  ( y  e.  U. x  <->  E. z
( y  e.  z  /\  z  e.  x
) )
54imbi2i 304 . . . . . 6  |-  ( ( y  e.  x  -> 
y  e.  U. x
)  <->  ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
65albii 1572 . . . . 5  |-  ( A. y ( y  e.  x  ->  y  e.  U. x )  <->  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) )
73, 6bitri 241 . . . 4  |-  ( x 
C_  U. x  <->  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) )
87anbi2i 676 . . 3  |-  ( ( x  =/=  (/)  /\  x  C_ 
U. x )  <->  ( x  =/=  (/)  /\  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) ) )
98exbii 1589 . 2  |-  ( E. x ( x  =/=  (/)  /\  x  C_  U. x
)  <->  E. x ( x  =/=  (/)  /\  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) ) )
102, 9mpbir 201 1  |-  E. x
( x  =/=  (/)  /\  x  C_ 
U. x )
Colors of variables: wff set class
Syntax hints:    -> wi 4    /\ wa 359   A.wal 1546   E.wex 1547    e. wcel 1717    =/= wne 2552    C_ wss 3265   (/)c0 3573   U.cuni 3959
This theorem is referenced by:  axinf2  7530
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1552  ax-5 1563  ax-17 1623  ax-9 1661  ax-8 1682  ax-6 1736  ax-7 1741  ax-11 1753  ax-12 1939  ax-ext 2370
This theorem depends on definitions:  df-bi 178  df-or 360  df-an 361  df-tru 1325  df-ex 1548  df-nf 1551  df-sb 1656  df-clab 2376  df-cleq 2382  df-clel 2385  df-nfc 2514  df-ne 2554  df-v 2903  df-dif 3268  df-in 3272  df-ss 3279  df-nul 3574  df-uni 3960
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