(defun quadratic (a b c)
(let ((d (- (* b b) (* 4 a c))))
(print (list 'discriminant d)); debug line
(cond
((> d 0)
(list "Solutions:"
(/ (+ (-b) (sqrt d)) (* 2 a))
(/ (- (-b) (sqrt d)) (* 2 a))))
((= d 0)
(list "Solution:"
(/ (-b) (* 2 a))))
(< d 0)
(list "No solution.")))))