a1 Department of Mathematics, Queens College and the Graduate School of CUNY, 33 West 42nd Street, New York, NY10036, USA
a2 IHES, 35 Rue de Chartres, 91440 Bures-sur-Yvette, France
Two Cr, r ≥ 2, expanding maps of the circle which are absolutely continuously conjugate are Cr conjugate. Here ƒ and g: S1 → S1 are expanding if they stretch tangent vectors in some metric, and a conjugacy is an isomorphism h: S1 → S1 such that fh = hg.
(Received January 12 1984)
(Revised October 08 1984)