Columbia subject headings:
Lobachevskiĭ, N. I. (Nikolaĭ Ivanovich), 1792-1856.
Mathematics--Philosophy.
Harvard subject headings:
Lobachevskiĭ, N. I. (Nikolaĭ Ivanovich), 1792-1856
Mathematics--Philosophy
Princeton subject headings:
Lobachevskiĭ, N. I. (Nikolaĭ Ivanovich), 1792-1856.
Mathematics--Philosophy.