We present a polynomial time algorithm for the unit disk covering problem with an approximation factor 72, and show that this is the best possible approximation factor based on the method used. This is an improvement on the best known approximation factor of 108.

The work considers the problem of solving a system of fuzzy relational equations with inf-implication composition and introduces the concepts of a characteristic matrix and attainable components. It is first shown that solving the system is closely related with the covering problem. Further, it is proved that maximal solutions of the system correspond to irredundant coverings of the characteris...