Syntax: SET HELP WORD
or      SET DIMEN(name) = expr
or      SET name = expr, expr [ ,expr ]
or      SET name = { list }
or      SET name = < list >
or      SET name = expr
or      SET name = expr IF ( expr )
or      SET name = expr1 ? expr2 : expr3
or      SET name[expr] = expr
or      SET name LOCAL
or      SET name = WORD( [ WORD , WORD ... ] )
or      SET IMAGE(expr1, expr2) = expr3
or      SET RANDOM s_expr

   SET HELP word sets the help string for a vector; the rest of the
line is read, and will be returned in response to a HELP WORD request,
or in the string-valued expression HELP(name).

   SET DIMEN(name) = expr declares name to be vector of size expr, and
initialises it to zero. This is only needed if a vector first appears
in an expression as a component, e.g. set x[3] = 10. Optionally you
can specify a type qualifier on the dimension, just like the ones
used to read columns: SET DIMEN(s) = 10.s will create a vector of
10 strings.

   SET name = expr1, expr2 [ ,expr3 ] initialises vector name to have
values running from expr1 to expr2, with an increment of expr3
(default: 1). This is essentially a DO loop, and could be written
as SET name = do(expr1, expr2) or SET name = do(expr1, expr2, expr3);
these forms having the advantage of being usable as parts of expressions.

   SET name = { list } or SET name = < list > set vector name to have
the values on the list, (e.g. SET x = < 1 2 3 4 132 >). Actually, the
{ list } is just an expression like any other, so SET x = 2*{1 2 3} +
4 is valid too. If the first item of the list is not a number the
vector is taken to be a string.

   SET name = expr sets the vector name to be equal to the expression
expr.  (See ARITHMETIC and LOGICAL). For string-valued vectors, the
only allowable expressions are a string enclosed in single quotes,
e.g. SET s='hello, world', or the CONCATenation of two string vectors.

   SET name = expr IF(expr) is similar, but only those elements of
expr which satisfy the IF clause are used. The resulting vector is
usually shorter than the starting expr.

   SET name = expr1 ? expr2 : expr3 is a little different. The
resulting vector is the same length as expr2 and expr3 (unless one is
a scaler), but consists of elements of expr2 and expr3 chosen
according as to whether expr1 is `true' (non-zero) or not.

   SET name[expr] = expr sets an element of a (pre-existing)
vector. Numerical expressions are converted to strings before being
assigned to string-valued vectors.

   SET name LOCAL makes name local, that is, it is visible only in the
current macro and macros called from it. If a vector of the same name
already exists it will be invisible until you leave the macro containing
the LOCAL command. You cannot set vectors to be LOCAL except in macros.

   SET name = WORD ( [ arg , arg ... ] ) calls the macro WORD with the
args in parentheses as its arguments (they are separated by commas and
can be words or numbers); The vector name is referred to as $0, (e.g.
SET $0=$1**2).

   SET IMAGE(expr1, expr2) = expr3 is used for setting elements of an image
(which must have been declared previously; see IMAGE). Expr1 and expr2 are
taken to be the (0-based) x- and y-indices of the desired points.

   SET RANDOM number sets the seed of the random number generator used
by the RANDOM operator; if you don't set it yourself it'll be set to
some value based on the time since 1970.

   See also CURSOR (for defining vectors using the cursor), DELETE for
deleting vectors, and LIST for listing vectors.