▁Com merce , ▁not ▁a ▁high ▁school , ▁and ▁thus ▁had ▁an ▁ins u fficient ▁qual ification ▁to ▁be ▁admitted ▁to ▁university . ▁However , ▁his ▁talent ▁did ▁not ▁remain ▁und et ected : ▁Ost row ski ' s ▁ment or , ▁ ▁D mit ry ▁Gra ve , ▁wrote ▁to ▁Land au ▁and ▁H ens el ▁for ▁help . ▁ ▁Sub sequently , ▁Ost row ski ▁began ▁to ▁study ▁mathematics ▁at ▁Mar burg ▁University ▁under ▁H ens el ' s ▁super vision ▁in ▁ 1 9 1 2 . ▁During ▁the ▁World ▁War ▁I ▁he ▁was ▁intern ed , ▁but ▁thanks ▁to ▁the ▁inter vention ▁of ▁H ens el , ▁the ▁restrictions ▁on ▁his ▁movements ▁were ▁e ased ▁somewhat , ▁and ▁he ▁was ▁allowed ▁to ▁use ▁the ▁university ▁library . ▁ ▁After ▁the ▁war ▁had ▁ended ▁Ost row ski ▁moved ▁to ▁Gött ingen ▁where ▁he ▁wrote ▁his ▁doctor al ▁dis sert ation ▁and ▁was ▁influenced ▁by ▁Hil bert , ▁Klein ▁and ▁Land au . ▁In ▁ 1 9 2 0 , ▁after ▁having ▁obtained ▁his ▁doctor ate , ▁Ost row ski ▁moved ▁to ▁Hamburg ▁where ▁he ▁worked ▁as ▁He cke ' s ▁assistant ▁and ▁finished ▁his ▁hab il itation ▁in ▁ 1 9 2 2 . ▁In ▁ 1 9 2 3 ▁he ▁returned ▁to ▁Gött ingen , ▁and ▁in ▁ 1 9 2 8 ▁became ▁Professor ▁of ▁Mathemat ics ▁at ▁Bas el , ▁until ▁ret irement ▁in ▁ 1 9 5 8 . ▁In ▁ 1 9 5 0 ▁Ost row