  Let rho and sigma be two central relations on a finite set A. It is known
that the clones Pol(rho) and Pol(sigma) which consists of all operations on A
that preserve rho respectively sigma are among the maximal clones on A. In this
paper, we find all central relations sigma such that the join clone of Pol(rho)
and Pol(sigma) is a maximal subclone of Pol(rho) where rho is a fixed central
relation.
