Absolute Parallelism in a Conformally Flat V_4* Vaiclav Hlavaty Indiana University Mathematics Journal 1965 text pdf 10.1512/iumj.1965.14.14001 10.1512/iumj.1965.14.14001 en Indiana Univ. Math. J. 14 (1965) 1 - 14 state-of-the-art mathematics http://iumj.org/access/