A. Yu. Olʹshanskii. Hyperbolicity of groups with subquadratic isoperimetric inequality. International Journal of Algebra and Computation, vol. 1 (1991), no. 3, pp. 281–289. MR1148230doi:10.1142/S0218196791000183
A. Yu. Olʹshanskii. Hyperbolicity of groups with subquadratic isoperimetric inequality. International Journal of Algebra and Computation, vol. 1 (1991), no. 3, pp. 281–289. MR1148230doi:10.1142/S0218196791000183