## Surjective function

### Set

 context $X,Y$ definiendum $f\in$ it inclusion $f:X\to Y$ postulate $\text{im}(f)=Y$

### Discussion

A function can only be or not be surjective w.r.t. to a stated codomain. A function is always surjective w.r.t. it's own image. See Function for further discussion.