eql
Major Section: PROGRAMMING
(remove1 x l) is l if x is not a member of l, else is the
result of removing the first occurrence of x from l.
The guard for (remove1 x l) requires l to be a true list and
moreover, either x is eqlablep or all elements of l are
eqlablep.
Also see remove, see remove1-equal, and see remove1-eq.