Joins of Inverse Semigroup Varieties and Band Varieties. - Peter R. Jones; Peter G. Trotter (Int. J. Algebra Comput., 1991)

Complete Congruences on Lattices of Varieties and of Pseudovarieties. - Francis Pastijn; Peter G. Trotter (Int. J. Algebra Comput., 1998)

A Combinatorial Property of Languages and Monoids. - Andrei V. Kelarev; Peter G. Trotter (Words, Languages & Combinatorics, 2000)