An almost isometric sphere theorem and weak strainers on Alexandrov spaces Qingsong Cai Indiana University Mathematics Journal 2017 text pdf 10.1512/iumj.2017.66.6073 10.1512/iumj.2017.66.6073 en Indiana Univ. Math. J. 66 (2017) 1267 - 1286 state-of-the-art mathematics http://iumj.org/access/