Countable Additivity of a Set Function Induced by Two Vector-Valued Measures M. Rao Indiana University Mathematics Journal 1972 text pdf 10.1512/iumj.1972.21.21068 10.1512/iumj.1972.21.21068 en Indiana Univ. Math. J. 21 (1972) 847 - 848 state-of-the-art mathematics http://iumj.org/access/