Rendiconti del Circolo Matematico di Palermo (1884-1940)December 1889, Volume 3, Issue 2, pp 51–53 | Cite asJournal de Mathématiques pures et appliquéesArticleFirst Online: 04 January 2009 16 Downloads This is a preview of subscription content, log in to check access.PreviewUnable to display preview. Download preview PDF.Unable to display preview. Download preview PDF.Copyright information© Springer 1889