Hyperbolic Extensions and Metrics ε-Close to Hyperbolic Pedro Ontaneda Indiana University Mathematics Journal 2017 text pdf 10.1512/iumj.2017.66.6026 10.1512/iumj.2017.66.6026 en Indiana Univ. Math. J. 66 (2017) 609 - 630 state-of-the-art mathematics http://iumj.org/access/