%0 Journal Article %A Richard O'Malley %T Strong essential cluster sets. %J Fundamenta Mathematicae %D 1973 %P 37-42 %V 78 %N 1 %I mathdoc %U http://geodesic.mathdoc.fr/articles/10.4064/fm-78-1-37-42/ %R 10.4064/fm-78-1-37-42 %G en %F 10_4064_fm_78_1_37_42