1. Analytical groups;Birkhoff, Garrett;Trans. Amer. Math. Soc.,1938
2. On one parameter groups of linear transformations;Dunford, Nelson;Ann. of Math. (2),1938
3. Semi-groups of operators and the Weierstrass theorem;Dunford, Nelson;Bull. Amer. Math. Soc.,1946
4. Note on continuous representations of Lie groups;Gårding, Lars;Proc. Nat. Acad. Sci. U.S.A.,1947
5. On one-parametrical groups of operators in a normed space;Gelfand, I.;C. R. (Doklady) Acad. Sci. URSS (N. S.),1939