Parameter Stack

DROP        a --
DUP         a -- a a
?DUP        DUP if a is nonzero
NIP         a b -- b
OVER        a b -- a b a
ROT         a b c -- b c a
SWAP        a b -- b a
TUCK        a b -- b a b
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
'S          Returns current stack pointer, not counting the
            push it's making right now.                 (cont.)