Neill, H. B. (1963). The art of contrary thinking: It pays to be contrary (6th and enl. ed.). Caxton Printers.
Dyfyniad Arddull ChicagoNeill, Humphrey B. The Art of Contrary Thinking: It Pays to Be Contrary. 6th and enl. ed. Caldwell, Idaho: Caxton Printers, 1963.
Dyfyniad MLANeill, Humphrey B. The Art of Contrary Thinking: It Pays to Be Contrary. 6th and enl. ed. Caxton Printers, 1963.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.