The authors

	Johan Mulderij Papenveld 1 NL-7475 DD Markelo The Netherlands tel. 0031-547-362755 fax. 0031-547-363889 e-mail : support@pro-gen.nl
	Dinant Scholte in't Hoff Burg. Korthals Alteslaan 12 NL-7475 DA Markelo The Netherlands tel. 0031-547-363152