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.
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S. M. Gersten (1992) studied this question.