%0 Journal Article %A Kôsaku Yosida %T The existence of the potential operator associated with an equicontinuous semigroup of class $(C_0)$ %J Studia Mathematica %D 1968 %P 531-533 %V 31 %N 5 %I mathdoc %U http://geodesic.mathdoc.fr/articles/10.4064/sm-31-5-531-533/ %R 10.4064/sm-31-5-531-533 %G en %F 10_4064_sm_31_5_531_533