Stasheff, Christopher. Her Majesty's Wizard
Summary: A grad student finds a manuscript which sends him to an another Earth where magic works and North Europe and most of Britain are covered with ice.
Published: Ballantine 1986 (0345274563).
Original in: English.
Translation: Italian by Annarita Guarnieri as Il mago di Sua Maestà, Nord 1987 (8842905178), Nord 1993 (884290743X).

Stasheff, Christopher. The Oathbound Wizard
Published: Ballantine 1993 (0345385470).

Stasheff, Christopher. The Witch Doctor
Published: Ballantine 1994 (034537584X), 1995 (0345388518); and SFBC 1994.

Stasheff, Christopher. The Secular Wizard
Published: Ballantine 1995 (0345376005, 0345388542).