yes,you got it right.I also know how to do some vc++(the old c++ not the new one with lambda,..).I know vb.net ok and also c++. I have asked a friend to help me in command line and probably when i show him my face next we will have a c++ program which readpolygons,readpoygons, perform union, write result polygons no graphics....so sad... ps:i have got 1 more library, in c of the previous decades.