Letwin, S. R. (1965). The pursuit of certainty. at the university Press.
Dyfyniad Arddull ChicagoLetwin, Shirley Robin. The Pursuit of Certainty. Cambridge: at the university Press, 1965.
Dyfyniad MLALetwin, Shirley Robin. The Pursuit of Certainty. at the university Press, 1965.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.