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We adopt the notion of combability of groups defined in 12. An example is given of a (bi-)combable group which is not residually finite. Two of the eight 3-dimensional geometries, Formula: see text and ℍ 2 ×ℝ, are quasiisometric. Seifert fibred manifolds over hyperbolic orbifolds have bicombable fundamental groups. Every combable group satisfies an exponential isoperimetric inequality.
S. M. Gersten (Tue,) studied this question.