%0 Journal Article %A Foiaş, Ciprian %T On Hille's spectral theory and operational calculus for semi-groups of operators in Hilbert space %J Compositio Mathematica %D 1959-1960 %P 71-73 %V 14 %I Kraus Reprint %U http://www.numdam.org/item/CM_1959-1960__14__71_0/ %G en %F CM_1959-1960__14__71_0