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Theorem inf2 7208
Description: Variation of Axiom of Infinity. There exists a non-empty set that is a subset of its union (using zfinf 7224 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 7207 . 2  |-  E. x
( x  =/=  (/)  /\  A. y ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
3 dfss2 3092 . . . . 5  |-  ( x 
C_  U. x  <->  A. y
( y  e.  x  ->  y  e.  U. x
) )
4 eluni 3730 . . . . . . 7  |-  ( y  e.  U. x  <->  E. z
( y  e.  z  /\  z  e.  x
) )
54imbi2i 305 . . . . . 6  |-  ( ( y  e.  x  -> 
y  e.  U. x
)  <->  ( y  e.  x  ->  E. z
( y  e.  z  /\  z  e.  x
) ) )
65albii 1554 . . . . 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 242 . . . 4  |-  ( x 
C_  U. x  <->  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) )
87anbi2i 678 . . 3  |-  ( ( x  =/=  (/)  /\  x  C_ 
U. x )  <->  ( x  =/=  (/)  /\  A. y
( y  e.  x  ->  E. z ( y  e.  z  /\  z  e.  x ) ) ) )
98exbii 1580 . 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 202 1  |-  E. x
( x  =/=  (/)  /\  x  C_ 
U. x )
Colors of variables: wff set class
Syntax hints:    -> wi 6    /\ wa 360   A.wal 1532   E.wex 1537    e. wcel 1621    =/= wne 2412    C_ wss 3078   (/)c0 3362   U.cuni 3727
This theorem is referenced by:  axinf2  7225
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10  ax-5 1533  ax-6 1534  ax-7 1535  ax-gen 1536  ax-8 1623  ax-11 1624  ax-17 1628  ax-12o 1664  ax-10 1678  ax-9 1684  ax-4 1692  ax-16 1926  ax-ext 2234
This theorem depends on definitions:  df-bi 179  df-or 361  df-an 362  df-tru 1315  df-ex 1538  df-nf 1540  df-sb 1883  df-clab 2240  df-cleq 2246  df-clel 2249  df-nfc 2374  df-ne 2414  df-v 2729  df-dif 3081  df-in 3085  df-ss 3089  df-nul 3363  df-uni 3728
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