Columbia subject headings:
Petrov, N. I. (Nikolaĭ Ivanovich), 1840-1921--Bibliography.
Harvard subject headings:
Petrov, N. I. (Nikolaĭ Ivanovich), 1840-1921--Bibliography.
Petrov, N. I. (Nikolaĭ Ivanovich), 1840-1921.
Scholars--Ukraine--Biography
Princeton subject headings: