Definition df-bday 27818

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 ∈ No ↦ dom 𝑥)

Detailed syntax breakdown of Definition df-bday

Step	Hyp	Ref	Expression
1		cbday 27815	. 2 class bday
2		vx	. . 3 setvar 𝑥
3		csur 27813	. . 3 class No
4	2	cv 1569	. . . 4 class 𝑥
5	4	cdm 5661	. . 3 class dom 𝑥
6	2, 3, 5	cmpt 5192	. 2 class (𝑥 ∈ No ↦ dom 𝑥)
7	1, 6	wceq 1570	1 wff bday = (𝑥 ∈ No ↦ dom 𝑥)

This definition is used by:  bdayval  27821  bdayfo  27850