ARRAY size
(ARRAY size origin)

	outputs an array of "size" members (must be a positive integer),
	each of which initially is an empty list.  Array members can be
	selected with ITEM and changed with SETITEM.  The first member of
	the array is member number 1 unless an "origin" input (must be an
	integer) is given, in which case the first member of the array has
	that number as its index.  (Typically 0 is used as the origin if
	anything.)  Arrays are printed by PRINT and friends, and can be
	typed in, inside curly braces; indicate an origin with {a b c}@0.

