Verifying Orientability of Rewrite Rules Using the Knuth-Bendix Order

We consider two decision problems related to the Knuth-Bendix order (KBO). The first problem is orientability: given a system of rewrite rules R, does there exist some KBO which orients every ground instance of every rewrite rule in R. The second problem is whether a given KBO orients a rewrite rule. This problem can also be reformulated as the problem of solving a single ordering constraint for the KBO. We prove that both problems can be solved in polynomial time. The algorithm builds upon an algorithm for solving systems of homogeneous linear inequalities over integers. Also we show that if a system is orientable using a real-valued KBO, then it is also orientable using an integer-valued KBO.