We consider equations of the type L lozenge Y = R, X lozenge Y = R, X(
lozenge n) = R, R lozenge X = L lozenge Y, where lozenge is a binary w
ord (language) operation, L, R are given constant languages and X, Y a
re the unknowns. We investigate the existence and uniqueness of maxima
l and minimal solutions, properties of solutions, and the decidability
of the existence of solutions. (C) 1996 Academic Press, Inc.