Selecting the intersection between two sets of macro variable lists

Hi,

I want to create a local variable list that is the union of 2 macro variable lists without repeat. Here is an example of what I would like:

Code:

global M1 "LogSize DY MOM36"
global M_crisis_1 "LogSize DY MOM12"

* What i want:
local union "LogSize DY MOM36 MOM12"

Thank you in advance!