Parameter Stack

DROP        a --
DUP         a -- a a
OVER        a b -- a b a
ROT         a b c -- b c a
SWAP        a b -- b a
2DROP       a a --
2DUP        a b -- a b a b
2OVER       a b c d -- a b c d a b
2SWAP       a b c d -- c d a b
PICK        Pick nth item from stack. "0 PICK" = DUP,
            "1 PICK" = OVER.
ROLL        Rotate PSP over n items. "1 ROLL" = SWAP,
            "2 ROLL" = ROT. 0 is noop.