BiLipschitz rough normal coordinates for surfaces with an $L^1$ curvature bound Joseph Fu 53B2053C2153C45biLipschitz parameters Indiana University Mathematics Journal 1998 text pdf 10.1512/iumj.1998.47.1527 10.1512/iumj.1998.47.1527 en Indiana Univ. Math. J. 47 (1998) 439 - 454 state-of-the-art mathematics http://iumj.org/access/