Test equality (of two numbers, symbols, or characters)
(eql x y) is logically equivalent to (equal x y).
Unlike equal, eql has a guard requiring at least one of
its arguments to be a number, a symbol, or a character. Generally, eql
is executed more efficiently than equal.
For a discussion of the various ways to test against 0, See zero-test-idioms.
Eql is a Common Lisp function. See any Common Lisp documentation for
(defun eql (x y)
(declare (xargs :guard (or (eqlablep x) (eqlablep y))))
(equal x y))