- document
- de Heer, Piet W. (author) report 1997
- document
- de Heer, Piet W. (author) report 1997
- document
- de Heer, Piet W. (author) report 1996
- document
- de Heer, Piet W. (author) report 1995
- document
- de Heer, Piet W. (author) report 1994
- document
- de Heer, Piet W. (author) report 1993
- document
- de Heer, Piet W. (author) report 1991
- document
- de Heer, Piet W. (author) report 1991
- document
- de Heer, Piet W. (author) report 1990
- document
- de Heer, Piet W. (author) report 1990
- document
- de Heer, Piet W. (author) report 1989
- document
- de Heer, Piet W. (author) report 1988
- document
- de Heer, Piet W. (author) report 1987
- document
- de Heer, Piet W. (author) report 1982
- document
- de Heer, Piet W. (author) report 1950