Helmut Seidl. Least and Greatest Solutions of Equations over . Nord. J. Comput., 3(1):41-62, 1996.

We consider the problem of computing least and greatest solutions of a system of equations , , over , i.e., the naturals (extended by ), where the right hand sides are expressions built up from constants and variables by various sets of operations. We present efficient algorithms in case where the following operations occur: (1) minimum and maximum; (2) maximum, addition and multiplication; (3) minimum, addition and multiplication; (4) minimum, maximum, addition and multiplication. We extend the methods to the cases where (one--sided) conditionals are allowed as well.