Set System Variable in a program

[Angus]

I didn't know that ja can mix non-rpn assignments. Wenn invoking functions their rpn notation is needed. Like with r->b(). I will dig into that, thanks.

Well, backspace acts as drop, however the main questin is about programming. I was initially under the impression that I have to use rpn notation for assignments (calling functions do) which would result in 2 on the stack. Then I would have needed a drop() command. Not a key.
If assignments can ideed be done in the a:=b notation that would be no issue.