@article {1991, title = {A class of absolute retracts of dwarf spheroidal galaxies}, journal = {Proc.Amer.Math.Soc. 112 (1991), no.2, 413}, number = {SISSA;79/89/M}, year = {1991}, publisher = {SISSA Library}, url = {http://hdl.handle.net/1963/837}, author = {Alberto Bressan and Arrigo Cellina and Andrzej Fryszkowski} }