On Sets of Integers Which Contain No Three Terms in Arithmetical Progression.

example there does not exist a sequence of domains Dl, D2, D3, . .. closing down on the point 0 and such that, for each n, the boundary of D. is compact. ,'Jones, F. B., "Concerning Certain Topologically Flat Spaces," Trans. Am. Math. Soc., 42, 53-93 (1937). 6 See Axiom 1. 6 See the proof of Theorem 1 of Chapter I. 7 See the proposition labeled "Theorem 25" in Chapter II. That this proposition is not a consequence of Axioms 0, 1 and 2 may be seen with the aid of Example 1.