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.