Z tries to prevent this by limiting all such subroutine names to one letter and three numbers. The letter must come first. Z is not usually case sensitive, although on an off day this could be an explanation of why your program isn't working. Subroutines must all be placed at the end of the program file, in reverse alpha, forward numerical order. You get used to it.
All calculations are in reverse polac notation a variant on reverse polish.
No warning of stack overflow is given. Stack overflow is directed to sensitive areas of the OS so you'll know when it happens.