$ clisp

<...snip...>

[1]> (load "quarto.l")
;; Loading file quarto.l ...
;;  Loading file lp.l ...
;;  Loaded file lp.l
;; Loaded file quarto.l
T
[2]> (task79--select-location-demo)
D    [B-] **** **** ****
C    **** [B+] **** ****
B    **** **** [b-] ****
A    **** **** **** [b+]
     1    2    3    4
On which cell will you place (R-), X?
(A1 A2 A3 B1 B2 B4 C1 C3 C4 D2 D3 D4)
> B3
That location cannot be chosen, please try again.
On which cell will you place (R-), X?
(A1 A2 A3 B1 B2 B4 C1 C3 C4 D2 D3 D4)
> d4
Location selected is D4
NIL
[3]> (bye)
Bye.