[Asselbergs 1968][Ausems 1964a][Ausems 1964b][Ausems 1965]
[De Haan 1975][De Haan & Van Delden 1979]
[Hendrickx 2012b]317-332
[Mak 1951]
[Scholtens 1952b]
[Van Mierlo 1940][Van Mierlo 1952][Van Stockum 1958][Vos 1963][Vos 1965a][Vos 1965b][Vos 1966][Vos 1967]
[Willems 1934]
