Columbia subject headings:
Ethics--Early works to 1800.
Plato. Protagoras.
Protagoras.
Socrates.
Harvard subject headings:
Ethics--Early works to 1800
Plato. Protagoras.
Protagoras
Socrates.
Princeton subject headings:
Ethics--Early works to 1800.
Plato. Protagoras.
Protagoras.
Socrates.