Residual finiteness of outer automorphism groups of certain 1-relator groups

Abstract

We prove that certain 1-relator groups have Property E. Using this fact, we characterize all conjugacy separable 1-relator groups of the form 〈a, b; (a -α b β a α b γ) t 〉, t ⩾ 1, having residually finite outer automorphism groups.