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.
