YES After renaming modulo { a->0, b->1, c->2, d->3 }, it remains to prove termination of the 4-rule system { 0 0 -> 1 2 , 1 1 -> 2 3 , 2 2 -> 3 3 3 , 3 3 3 -> 0 2 } The system was filtered by the following matrix interpretation of type E_J with J = {1,...,2} and dimension 2: 0 is interpreted by / \ | 1 30 | | 0 1 | \ / 1 is interpreted by / \ | 1 27 | | 0 1 | \ / 2 is interpreted by / \ | 1 32 | | 0 1 | \ / 3 is interpreted by / \ | 1 21 | | 0 1 | \ / After renaming modulo { }, it remains to prove termination of the 0-rule system { } The system is trivially terminating.