Делали с ребёнком домашку... Вот такой вот первый класс.

gistfile1.lisp

(let ((points '("a" "b" "v" "g" "d" "e" "i" "j" "z"))
      (edges '("ab" "ae" "av" "ag" "ad"
	       "ba" "be" "bi" "bv" "bg" "bd"
	       "vb" "vg" "vi" "vj" "va" "vd"
	       "gv" "gd" "gj" "gz" "gb" "ga"
	       "dg" "dz" "dv" "db" "da"
	       "ea" "eb" "ei" "ej" "ez"
	       "ie" "ib" "iv" "ij" "iz"
	       "ji" "jv" "jg" "jz" "je"
	       "zj" "zg" "zd" "zi" "ze"))
      (count 0)
      (q nil))
  (loop
   for p1 in points
   do (loop
       for p2 in points
       do (loop
	   for p3 in points
	   do (loop
	       for p4 in points
	       do (when (and (string/= p1 p2)
			     (string/= p1 p3)
			     (string/= p1 p4)
			     (string/= p2 p3)
			     (string/= p2 p4)
			     (string/= p3 p4)
			     (member (concatenate 'string p1 p2) edges :test #'string=)
			     (member (concatenate 'string p2 p3) edges :test #'string=)
			     (member (concatenate 'string p3 p4) edges :test #'string=)
			     (member (concatenate 'string p4 p1) edges :test #'string=)
			     (not (member (concatenate 'string p1 p2 p3 p4) q :test #'string=))
			     (= 2 (length (intersection (list p1 p2 p3 p4) '("a" "b" "v" "g" "d") :test #'string=)))
			     (= 2 (length (intersection (list p1 p2 p3 p4) '("e" "i" "j" "z") :test #'string=))))
		    (push (concatenate 'string p1 p2 p3 p4) q)
		    (push (concatenate 'string p2 p3 p4 p1) q)
		    (push (concatenate 'string p3 p4 p1 p2) q)
		    (push (concatenate 'string p4 p1 p2 p3) q)
		    (push (concatenate 'string p4 p3 p2 p1) q)
		    (push (concatenate 'string p3 p2 p1 p4) q)
		    (push (concatenate 'string p2 p1 p4 p3) q)
		    (push (concatenate 'string p1 p4 p3 p2) q)

		    (format t "~A ~A ~A ~A~%" p1 p2 p3 p4)
		    (incf count))))))
  (format t "count = ~A~%" count))

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