Major Section: PROGRAMMING
(Union-eq x y) equals a list whose members (see member-eq) contains the
members of x and the members of y. More precisely, the resulting
list is the same as one would get by first deleting the members of y from
x, and then concatenating the result to the front of y.
The guard for union-eq requires both arguments to be true lists and
at least one to be a true list of symbols, as the function member-eq is
used to test membership (with eq). See union-equal.