1999
(12) — Islamic Mysticism Contested. Thirteen Centuries of Controversies and Polemics (together with Frederick De Jong). Leiden 1999. XVI, 829 S.
(13) — Fritz Meier: Essays on Islamic Piety and Mysticism. Translated by John O’Kane with Editorial Assistance of Bernd Radtke. Leiden 1999. XX, 750 S.
(14) — The Exoteric Aḥmad Ibn Idrīs. A Sufi’s Critique of the Madhāhib and the Wahhābīs (together with John O’Kane, Knut S. Vikør & R.S. O’Fahey). Leiden 1999. X, 225 arab.- engl. S.
