Description: If a mapping is a set, its domain is a set. (Contributed by NM, 27-Aug-2006) (Proof shortened by Andrew Salmon, 17-Sep-2011)
Ref | Expression | ||
---|---|---|---|
Assertion | dmfex | |- ( ( F e. C /\ F : A --> B ) -> A e. _V ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | fdm | |- ( F : A --> B -> dom F = A ) |
|
2 | dmexg | |- ( F e. C -> dom F e. _V ) |
|
3 | eleq1 | |- ( dom F = A -> ( dom F e. _V <-> A e. _V ) ) |
|
4 | 2 3 | syl5ib | |- ( dom F = A -> ( F e. C -> A e. _V ) ) |
5 | 1 4 | syl | |- ( F : A --> B -> ( F e. C -> A e. _V ) ) |
6 | 5 | impcom | |- ( ( F e. C /\ F : A --> B ) -> A e. _V ) |