Gerbert of Aurillac’s Letter on the Area of an Equilateral Triangle: Philosophical and Theological Perspective. Epistola a Gerberto abbate Bobiensi et fortasse jam archiepiscopo Ravennae ad Adelboldum de causa diversitatis arearum trigoni aequilateri geometrice arithmeticeve expensi, Trans. by Aleksandr A. Artamonov