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https://liveyourmaths.com/2016/08/10/%ce%bd%ce%b9%ce%ba%ce%bf%ce%bb%ce%ac%ce%b9-%ce%bb%ce%bf%ce%bc%cf%80%ce%b1%cf%84%cf%83%ce%ad%cf%86%cf%83%ce%ba%cf%85-1792-1856-nikolai-i-lobachevsky/
Νικολάι Λομπατσέφσκυ, 1792-1856 (Nikolai I. Lobachevsky)