Description: A function's value belongs to its codomain. (Contributed by Mario Carneiro, 29-Dec-2016)
Ref | Expression | ||
---|---|---|---|
Hypothesis | ffvelrnd.1 | |- ( ph -> F : A --> B ) |
|
Assertion | ffvelrnda | |- ( ( ph /\ C e. A ) -> ( F ` C ) e. B ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ffvelrnd.1 | |- ( ph -> F : A --> B ) |
|
2 | ffvelrn | |- ( ( F : A --> B /\ C e. A ) -> ( F ` C ) e. B ) |
|
3 | 1 2 | sylan | |- ( ( ph /\ C e. A ) -> ( F ` C ) e. B ) |