Write a function in ML

(e) union

This function returns the union of two sets. For example, union((3,[2,7,4]), (2,[7,3])) may return (4,[4,2,3,7]) because {2, 7, 4} {7, 3} = {4, 2, 3, 7}.

sample execution

val union = fn : (int * int list) * (int * int list) -> int * int lis

- val S' = (3,[4,2,7]);

val S' = (3,[4,2,7]) : int * int list

- val U = (2,[7,3]);

val U = (2,[7,3]) : int * int list

union(S,U);

val it = (4,[4,2,7,3]) : int * int list