TransliterationGavriil Semikolenov. Etyudy po geometrii Lobachevskogo Etyud 1: Teorema Pifagora v geometrii Lobachevskogo.
In EnglishGavriil Semikolov. Studies on Lobachevsky geometry Study 1: Pythagoras theorem in Lobachevsky geometry. In Russian (ask us if in doubt)
$399