%%graph_to_change([[X,Y1],[X,Y2]],+) :-
%%	Y2 is Y1+1.

graph_to_change(Graph1,Graph2,Change) :-
	find_height(Graph1,Height1), find_height(Graph2,Height2),
	(
		(Height2 >= Height1, Change='+');
		(Height2 < Height1, Change='-')
	).
find_height(Graph,Height) :-
	find_minimum(Graph,Minimum), find_maximum(Graph,Maximum),
	Height is Maximum-Minimum.

find_minimum([Value|List],Minimum) :-
	find_minimum(Value,List,Minimum).
find_minimum(Minimum,[],Minimum).
find_minimum(Value,[Value1|List],Minimum) :-
	(Value1>=Value, find_minimum(Value,List,Minimum));
	(Value1<Value, find_minimum(Value1,List,Minimum)).

find_maximum([Value|List],Maximum) :-
        find_maximum(Value,List,Maximum).
find_maximum(Maximum,[],Maximum).
find_maximum(Value,[Value1|List],Maximum) :-
        (Value1=<Value, find_maximum(Value,List,Maximum));
        (Value1>Value, find_maximum(Value1,List,Maximum)).