Often one wants to build up a list incrementally; this is
usually done using ` cons`.

Note that for any *x*,
` (cons ` *x* ` '())` = ` (list ` *x* ` )` :

(cons 'a '()) = (a)(cons '(a) '()) = ((a))

If *lst* is a list, then ` (cons` *x lst*` )`
will make a new list with *x* as its first element, followed by
the other elements of *lst*.

(cons 'a '(b c)) = (a b c)(cons '(a) '(b c)) = ((a) b c)