Vector Algebras and Potentials Fletcher DonaldsonW. LongW. McCulleyRoger OsbornE. TittL. Worthington Indiana University Mathematics Journal 1953 text pdf 10.1512/iumj.1953.2.52021 10.1512/iumj.1953.2.52021 en Indiana Univ. Math. J. 2 (1953) 413 - 442 state-of-the-art mathematics http://iumj.org/access/