His pupil and assistant was Wynrich of Wesel , and art historian Johann Matthias Firmenich - Richartz , in particular , has ascribed to Wynrich pictures attributed to Wilhelm .
Aldenhoven and others have protested against this ascription .
His pupil and assistant was Wynrich of Wesel , and art historian Johann Matthias Firmenich - Richartz , in particular , has ascribed to Wynrich pictures attributed to Wilhelm , although Aldenhoven and others have protested against this ascription .