Meet-reducible submaximal clones determined by two central relations
  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. 
Jeufack L.T. Yannick, Luc E. F. Diekouam and Etienne R. A. Temgoua
math.RA