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Definition df-bday 25592
Description: Finally, we introduce the birthday function. This function maps each surreal to an ordinal. In our implementation, this is the domain of the sign function. The important properties of this function are established later. (Contributed by Scott Fenton, 11-Jun-2011.)
Assertion
Ref Expression
df-bday  |-  bday  =  ( x  e.  No  |->  dom  x )

Detailed syntax breakdown of Definition df-bday
StepHypRef Expression
1 cbday 25589 . 2  class  bday
2 vx . . 3  set  x
3 csur 25587 . . 3  class  No
42cv 1651 . . . 4  class  x
54cdm 4870 . . 3  class  dom  x
62, 3, 5cmpt 4258 . 2  class  ( x  e.  No  |->  dom  x
)
71, 6wceq 1652 1  wff  bday  =  ( x  e.  No  |->  dom  x )
Colors of variables: wff set class
This definition is referenced by:  bdayval  25595  bdayfo  25622
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