We prove that if every hyperbolic group is residually finite, then every
quasi-convex subgroup of every hyperbolic group is separable. The main tool is
relatively hyperbolic Dehn filling.Comment: (v1) 22 pages, 2 figures. (v2) 24 pages, 2 figures. An error in the
proof and statement of the main technical lemma was corrected, and some other
small corrections and clarifications were mad