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Definition df-bday 25513
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 25510 . 2  class  bday
2 vx . . 3  set  x
3 csur 25508 . . 3  class  No
42cv 1648 . . . 4  class  x
54cdm 4837 . . 3  class  dom  x
62, 3, 5cmpt 4226 . 2  class  ( x  e.  No  |->  dom  x
)
71, 6wceq 1649 1  wff  bday  =  ( x  e.  No  |->  dom  x )
Colors of variables: wff set class
This definition is referenced by:  bdayval  25516  bdayfo  25543
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