On the Extension of Harmonic Functions in Three Variables H. Lewy Indiana University Mathematics Journal 1965 text pdf 10.1512/iumj.1965.14.14059 10.1512/iumj.1965.14.14059 en Indiana Univ. Math. J. 14 (1965) 925 - 927 state-of-the-art mathematics http://iumj.org/access/