If you're afraid of forgetting something, write it down. Surely I do that. Here is what I found today in my notes:
pstops "2:0L@.7(21cm,0)+1L@.7(21cm,14.85cm)" input.ps output.ps
I think what it does is convert a postscript document from simple A4 document to two pages on one A4. But it's just a guess… because I didn't write down what it does.