Columbia subject headings:
Chaadaev, P. I︠A︡. (Petr I︠A︡kovlevich), 1794-1856.
Harvard subject headings:
Chaadaev, P. I︠A︡. (Petr I︠A︡kovlevich), 1794-1856
Chaadnev, Petr I͡Akovlevīch, 1794-1856.
Princeton subject headings:
Chaadnev, Petr I︠A︡kovlevīch, 1794-1856.