Commutators with Fractional Differentiation and BMO Sobolev Spaces Margaret Murray Indiana University Mathematics Journal 1985 text pdf 10.1512/iumj.1985.34.34012 10.1512/iumj.1985.34.34012 en Indiana Univ. Math. J. 34 (1985) 205 - 215 state-of-the-art mathematics http://iumj.org/access/