transport(Venise,300)->;
transport(Londre,400)->;
transport(NewYork,500)->;

sejour(Venise,etoile1,1000)->;
sejour(Venise,etoile2,2000)->;
sejour(Venise,etoile3,3000)->;

sejour(Londre,etoile1,1500)->;
sejour(Londre,etoile2,2000)->;
sejour(Londre,etoile3,2500)->;

sejour(NewYork,etoile1,2000)->;
sejour(NewYork,etoile2,3000)->;
sejour(NewYork,etoile3,4000)->;

duree(1)->;
duree(2)->;
duree(3)->;

calculprix(c,c1,c2,m)->val(add(c1,mul(c2,m)),c);
voyage(v,h,d,f)->transport(v,f1)
                 sejour(v,h,f2)
		 calculprix(f,f1,f2,d);

calcul_prix(c,c1,c2,m)->val(add(c1,mul(c2,m)),c);

/* Note:  m = f_max */

economique(v,h,d,f,m)->duree(d)
		voyage(v,h,d,f)
		val(inf(f,m),1);


voyageConomique(v,h,d,f,m)->peut_on(v,h,1,d,f,m);

peut_on(v,h,d,d,f,m)->voyage(v,h,d,f)
			val(inf(m,f),0);

peut_on(v,h,d1,d,f,m)->voyage(v,h,d1,f1)
			val(f1 '>' m, 0)
			val(d1+1,d2)
			peut_on(v,h,d2,d,f,m);