 In 1961 Milnor disproved the Hauptvermutung by illustrating two simplicial complexes that are homeomorphic but combinatorially distinct.He introduced the growth invariant in a finitely presented group and the theorem stating that the fundamental group of a negatively curved Riemannian manifold has exponential growth became a striking point in the foundation for modern geometric group theory, and the basis for the theory of a hyperbolic group in 1987 by Mikhail Gromov.In 1984 Milnor introduced a definition of attractor.