- document
- Beukelman, Wim (author), Keuning, Lex (author) report 1986
- document
- Beukelman, Wim (author), Keuning, Lex (author) report 1985
- document
- Beukelman, W. (author), Keuning, P.J. (author), Huijsmans, R.H.M. (author) report 1983
- document
- Beukelman, W. (author), Huijsmans, R.H.M. (author), Keuning, P.J. (author) journal article 1983
- document
- Beukelman, Wim (author), Keuning, Lex (author) conference paper 1975