• [1] Andrew Bruckner, Minimal superadditive extensions of superadditive functions, Pacific J. Math. 10 (1960), 1155–1162. MR 0122943 (23 #A275)
• [2] Einar Hille and Ralph S. Phillips, Functional analysis and semi-groups, American Mathematical Society Colloquium Publications, vol. 31, American Mathematical Society, Providence, R. I., 1957. rev. ed. MR 0089373 (19,664d)
• [3] R. A. Rosenbaum, Sub-additive functions, Duke Math. J. 17 (1950), 227–247. MR 0036796 (12,164a)

Bibliography

[1]

Andrew Bruckner, Minimal superadditive extensions of superadditive functions, Pacific J. Math. 10 (1960), 1155-1162. MR 0122943 (23:A275)

[2]

E. Hille and R. Phillips, Functional analysis and semigroups, Chapter VII, pp. 237-255, Amer. Math. Soc. Colloq. Publ., Vol. 31, Amer. Math. Soc., Providence, R. I., 1957. MR 0089373 (19:664d)

[3]

R. A. Rosenbaum, Subadditive functions, Duke Math. J. 17 (1950), 227-247. MR 0036796 (12:164a)