But even while he was writing on these topics, papers on surfaces were still appearing, and differential geometry absorbed nearly all his attention for the last twelve years or so of his life.
Ngunit kahit na habang siya ay sumusulat sa mga paksa, mga papeles sa ibabaw ay pa rin lumalabas, at kaugalian geometry buyo halos lahat ng kanyang atensiyon para sa huling labindalawang taon o kaya ng kanyang buhay.