sbcl illegal function call - syntax-error

Question

I decided reading SICP a little, just to see what it is all about (I am not MIT student, actually already almost done with studying, this is no homework, but the content might be homework for someone.). Since I have installed sbcl, I have to change syntax a little, compared to the book. However, I don't understand why my solution to exercise 1.3 is not working:
(defun square (x) (* x x))
(defun sum-of-squares (x y)
(+ (square x) (square y)))
(defun sum-of-squares-two-max (x y z) (
(cond
((eq (min x y z) x) (sum-of-squares y z))
((eq (min x y z) y) (sum-of-squares x z))
(t (sum-of-squares x y))
)))
To load this I run sbcl --load exercise-1.3.lisp. When I load it, I get the error:
; file: /home/xiaolong/development/LISP/SICP/exercise-1.3.lisp
; in: DEFUN SUM-OF-SQUARES-TWO-MAX
; ((COND ((EQ (MIN X Y Z) X) (SUM-OF-SQUARES Y Z))
; ((EQ (MIN X Y Z) Y) (SUM-OF-SQUARES X Z)) (T (SUM-OF-SQUARES X Y))))
;
; caught ERROR:
; illegal function call
; (DEFUN SUM-OF-SQUARES-TWO-MAX (X Y Z)
; ((COND ((EQ # X) (SUM-OF-SQUARES Y Z)) ((EQ # Y) (SUM-OF-SQUARES X Z))
; (T (SUM-OF-SQUARES X Y)))))
;
; caught STYLE-WARNING:
; The variable X is defined but never used.
;
; caught STYLE-WARNING:
; The variable Y is defined but never used.
;
; caught STYLE-WARNING:
; The variable Z is defined but never used.
;
; compilation unit finished
; caught 1 ERROR condition
; caught 3 STYLE-WARNING conditions
Multiple things I don't understand:
Why are some variables not used? I use all of them in the conditional ...
Why is a function call illegal? How can I compose functions if I cannot call a function from inside a function? (I probably can, but I am doing it wrong?)
When I comment out the third function, it loads without errors.
I checked the syntax for the conditional multiple times already, cannot find the mistake.
How can I correct this code?

Answer 1

Get rid of the extra open paren.
(defun sum-of-squares-two-max (x y z)
(cond
((eq (min x y z) x) (sum-of-squares y z))
((eq (min x y z) y) (sum-of-squares x z))
(t (sum-of-squares x y))))
The issue is that, with the paren, the code will call whatever your cond will evaluate to (as with all first items within parens). Without the paren, it knows that the result of the function is whatever the cond evaluates to.
Also, a general warning: SICP uses scheme, so you'll see some small differences between the book and what common lisp macros force you into.