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Definition df-bday 30105
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 30102 . 2  class  bday
2 vx . . 3  setvar  x
3 csur 30100 . . 3  class  No
42cv 1404 . . . 4  class  x
54cdm 4823 . . 3  class  dom  x
62, 3, 5cmpt 4453 . 2  class  ( x  e.  No  |->  dom  x
)
71, 6wceq 1405 1  wff  bday  =  ( x  e.  No  |->  dom  x )
Colors of variables: wff setvar class
This definition is referenced by:  bdayval  30108  bdayfo  30135
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