Collective L Estimates for Families of Functions with Orthonormal Derivatives Peter Constantin Indiana University Mathematics Journal 1987 text pdf 10.1512/iumj.1987.36.36032 10.1512/iumj.1987.36.36032 en Indiana Univ. Math. J. 36 (1987) 603 - 616 state-of-the-art mathematics http://iumj.org/access/