How to use boolean intersect with two plans and the mirror modifier These are two plans I want to cut to only keep the outside of the vertical plane. There is a mirror modifier applied on z axe. I tried to use the 
Boolean Intersect Tool. So my question is how to use one plane (object) as a cutter to cut away from another plane (object).


I removed the mirror modifier and tried with 3D object but nothing happens as I hit CTRL+ F key Intersect(Boolean). I tried with the Intersect knife tool and "No Intersection found" diplays.
Thanks for your help.
Finally I found the problem: Boolean Intersect (and Knife Tool)  work only if the objects are joined.