(setf G1 '( 	(A B 60) (A E 12)
	    	(B C 61) (B F 1)
		(C D 62) (C G 4)
		(D H 15)
		(E F 2) (E I 70)
		(F G 3) (F J 6)
		(G H 5) (G K 72)
		(H L 64)
		(I J 7) (I M 69)
		(J K 8) (J N 11)
		(K L 9) (K O 10)
		(L P 65)
		(M N 13) 
		(N O 67)
		(O P 14) ) )


(setf G2 '(	(A B 1) (A C 4) (A D 5)
		(B C 2) (B D 5)
		(C D 3) ) )


(untrace)

(print (min_spanning_tree G2))
; -> should generate a tree of cost 6

(print (min_spanning_tree G1))
; -> should generate a tree of cost 120