Fibonacci groups, F(2,n), are hyperbolic for n odd and n >= 11

Abstract

We prove that the Fibonacci group, F(2,n), for n odd and n >= 11 is hyperbolic. We do this by applying a curvature argument to an arbitrary van Kampen diagram of F(2,n) and show that it satisfies a linear isoperimetric inequality. It then follows that F(2, n) is hyperbolic.