Department of Mathematics/Boole Centre for Research in Informatics, University College Cork, Cork, Ireland. jm20@proba.ucc.ie|Department of Mathematics/Boole Centre for Research in Informatics, University College Cork, Cork, Ireland. jm20@proba.ucc.ie|Department of Mathematics/Boole Centre for Research in Informatics, University College Cork, Cork, Ireland. jm20@proba.ucc.ie