Operators between subspaces and quotients of $L^1$ G. GodefroyN. KaltonDening Li 46A2246B2046B2543A1543A4660E07integral representation of operators on $L^1$small into-isomorphisms of $L^1$complemented subspaces of $L^1$isometries of $L^1$small subspaces of $L^1$nicely placed subspaces of $L^1$semi-Riesz setsstrong Enflo operatorsDaugavet operators Indiana University Mathematics Journal 2000 text pdf 10.1512/iumj.2000.49.1753 10.1512/iumj.2000.49.1753 en Indiana Univ. Math. J. 49 (2000) 245 - 286 state-of-the-art mathematics http://iumj.org/access/