€ 6,00
24 p. Wrappers. (Valedictory lecture)
Groningen, Batavia, Wolters, 1947.
aard
Berkeley & Los Angeles, University of California Press, 1957.
Kampen, Kok, 1953.
Groningen, Djakarta, Wolters, 1957.
Ann Arbor, Univ. of Michigan Press, (1959).