Oscar Halecki (1957). Poland. New York: Frederick A. Praeger. Archived from the original on 29 March 2020. Retrieved 29 March 2020. – via Questia (نیازمند آبونمان)
Oscar Halecki (1957). Poland. New York: Frederick A. Praeger. Archived from the original on 29 March 2020. Retrieved 29 March 2020. – via Questia (نیازمند آبونمان)