In one aspect of the invention, a computer system comprises application logic executable to search an optical medium for at least one type of file system that may be resident on the optical medium. The animal litter generally includes corn cob, a lubricant, and a cohesiveness agent. Methods for the construction of such a membrane are also provided. The call is placed to a destination corresponding to a service having a service area. A control unit controls the displacing unit based of a result of detecting the toner pattern by the toner-pattern detecting unit. Therefore, the light curtain generating device can readily adapt itself to each particular application at low cost and in a highly precise manner.