Types of reductive monoids

Let M be a reductive monoid with a reductive unit group G. Clearly there is a natural G x G action on M. The orbits are the J-classes (in the sense of semigroup theory) and form a finite lattice. The general problem of findin g the lattice remains open. In this paper we study a new class of reductive monoids constructed by multilined closure. We obtain a general theorem to determine the lattices of these monoids. We find that the (J, sigma)-irredu cible monoids of Suzuki type and Ree type belong to this new class. Using t he general theorem we then list all the lattices and type maps of the (J, s igma)-irreducible monoids of Suzuki type and Ree type. (C) 1999 Academic Pr ess.