- document
- de Jong, J.L. (author), van Ingen Schenau, H.A. (author), Pietersen, O.B.M. (author) report 1969
- document
- de Jong, J.L. (author), van Ingen Schenau, H.A. (author), Pietersen, O.B.M. (author), Doekes, G. (author), van Eek, G.M. (author) report 1969
- document
- de Jong, J.L. (author), van Ingen Schenau, H.A. (author), Pietersen, O.B.M. (author) report 1969