Reposting code like >>>/gulag/633 suggested:

(define (groessere-quadratsumme x y z)
(define (quadratsumme a b) (+ (* a a) (* b b)))
(cond ((and (< x y) (< x z)) (quadratsumme y z))
((and (< y x) (< y z)) (quadratsumme x z))
((and (< z x) (< z y)) (quadratsumme x y))
((= x y) (cond ((< x z) (quadratsumme x z))
(else (quadratsumme x x))))
((= z y) (cond ((> x z) (quadratsumme x z))
(else (quadratsumme z z))))))

By the way, if you wonder what's the matter with LISP and GNU, GNU Emacs, one of first and most important programs of the GNU project is written in a certain LISP dialect, which makes it more extensible. Based on the experiences with that, Guile was created as a LISP interpreter that is easy to include in other software as a extension language. Also, the board of the FSF contains people like Sussman, who has designed Scheme LISP.