% a way to find the minimum cost of car insurance
% minimum(+Company, +Cost): Cost is minimum over all insurance(Company, Cost)
:-dynamic(mini/2). % mini(C,V) asserts the minimum so far is C,S.

minimum(C,V):-insurance(C0,V0),asserta(mini(C0,V0)), !, minimumrest(C,V).

minimumrest(_,_):-insurance(C1,V1), retract(mini(C0,V0)), 
	( V1 < V0 , asserta(mini(C1,V1)) ;
          V1 >=V0 , asserta(mini(C0,V0))
	), fail.
minimumrest(C,V):-retract(mini(C,V)).

insurance('AAA', 900).
insurance('GEICO', 800).
insurance('MobCo', 1000).
:-write('example: minimum(Company,Cost).').