John Meakin (2007). "Groups and semigroups: connections and contrasts". In C.M. Campbell; M.R. Quick; E.F. Robertson; G.C. Smith (eds.). Groups St Andrews 2005 Volume 2. Cambridge University Press. p.367. ISBN978-0-521-69470-4. preprint citing Lawson, M. V. (1998). "The Möbius Inverse Monoid". Journal of Algebra. 200 (2): 428–438. doi:10.1006/jabr.1997.7242.
John Meakin (2007). "Groups and semigroups: connections and contrasts". In C.M. Campbell; M.R. Quick; E.F. Robertson; G.C. Smith (eds.). Groups St Andrews 2005 Volume 2. Cambridge University Press. p.367. ISBN978-0-521-69470-4. preprint citing Lawson, M. V. (1998). "The Möbius Inverse Monoid". Journal of Algebra. 200 (2): 428–438. doi:10.1006/jabr.1997.7242.