a_star :: PathContext :: heuristic_cost
	# Heuristic
	fun heuristic_cost(a, b: N): Int is abstract
					lib/a_star/a_star.nit:352,2--353,45
				
	redef fun heuristic_cost(a, b) do return 0
					lib/a_star/a_star.nit:372,2--43
				
	redef fun heuristic_cost(a, b) do return 0
					lib/a_star/a_star.nit:401,2--43