The arithmeticity of the figure eight knot orbifolds

Abstract

Continuing their investigation [in Topology '90 (Columbus, OH, 1990), 133–167, de Gruyter, Berlin, 1992;] of the problem of how rarely a hyperbolic orbifold is arithmetic, the authors classify the arithmetic figure eight orbifolds: there are exactly six among the hyperbolic figure eight orbifolds (K,n), n>3. This relies on work by H. Helling, A. C. Kim and J. L. Mennicke ["On Fibonacci groups'', Preprint; per bibl.] and extends a recent result of A. Reid [J. London Math. Soc. (2) 43 (1991), no. 1, 171–184;] that (K,∞) is the only arithmetic knot complement.