Thomas Merz writes: What is it? An excerpt from a debugging session? PostScript-beginners first trial-and-exec? No! This is the smallest piece of selfreproducing code (that I know of). It elegantly shows the interchangeability of code and data in the PostScript language. Except for minor changes it is fully portable (on some interpreters you have to change the blanks before and after brackets and curly braces). How does it work? The procedure in the first line is used as data which is output to %stdout. Then, the procedure is used as code which is executed. What does this code do? It outputs the second line and flushes the output channel. That's it! the {(pstack exec) = flush} goes entirely to the stack as a procedure. the pstack prints it. And then the "exec" executes the procedure, printing "pstack exec". As you know, selfreproducing code is one of the key issues in the survey of computer viruses. While I am not going to spread PostScript viruses among printers and other devices, I think it's a sort of intellectual challenge and training of programming skills to develop selfreproducing code.