On sortable intervals of monomials

In 1996, in his study of Gröbner bases of toric ideals, Sturmfels introduced a sorting operator on pairs of monomials of degree d in n variables. This gave rise to the notion of sortable sets, namely sets B of monomials of degree d such that B×B is preserved by that operator. In this paper, we determine all lex-intervals or revlex-intervals of monomials which are sortable. The solution involves the notion of greatest common prefix.