Description: The birthday function's domain is No . (Contributed by Scott Fenton, 14-Jun-2011)
Ref | Expression | ||
---|---|---|---|
Assertion | bdaydm | ⊢ dom bday = No |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bdayfo | ⊢ bday : No –onto→ On | |
2 | fof | ⊢ ( bday : No –onto→ On → bday : No ⟶ On ) | |
3 | 1 2 | ax-mp | ⊢ bday : No ⟶ On |
4 | 3 | fdmi | ⊢ dom bday = No |