Union of two sets or of two lists : union

union is an infixed operator.
union takes as argument two sets or two lists union returns the union set of the arguments.
Input :

set[1,2,3,4] union set[5,6,3,4]

Or :

%{1,2,3,4%} union %{5,6,3,4%}

Output :

1,2,3,4,5,6

Input :

[1,2,3] union [2,5,6]

Output :

1,2,3,5,6