On Hadamard's Variation Formula for Green's Function S. Warschawski Indiana University Mathematics Journal 1960 text pdf 10.1512/iumj.1960.9.59028 10.1512/iumj.1960.9.59028 en Indiana Univ. Math. J. 9 (1960) 497 - 511 state-of-the-art mathematics http://iumj.org/access/