; (title cost town street)
; prod for producer
(setf prod '(
    ("a" 10 "1" "$")
    ("a" 6 "4" "$")
    ("a" 15 "8" "$")

    ("b" 200 "5" "@")
    ("b" 180 "1" "@")
    ("b" 300 "7" "@")

    ("c" 31 "6" "%")
    ("c" 28 "4" "%")
    ("c" 28 "5" "%")
    )
)

(setf goods '(
    "b"
    "c"
    )
)

(defun min_cost_prod (p)
    (cond
        ((null (cdr p)) (car p))
        ((< (cadar p) (cadr (min_cost_prod (cdr p)))) (car p))
        (t (min_cost_prod (cdr p)))
    )
)

(defun goods_prod (g p)
    (cond
        ((null p) nil)
        ((equal g (caar p)) (cons (car p) (goods_prod g (cdr p))))
        (t (goods_prod g (cdr p)))
    )
)

(defun nice_prod (g p)
    (cond
        ((null g) nil)
        (t (cons (min_cost_prod (goods_prod (car g) p)) (nice_prod (cdr g) p)))
    )
)

(print (nice_prod goods prod))