arXiv subjects
Publications and source records attributed to Colin C. Graham.
New sets (typically found by computer search) with Sidon constant equal to the square root of their cardinalities are given. For each integer $N$ there are only a finite number of groups of prime order containing $N$-element extreme sets. Some extreme sets appear to fit a pattern; others do not. Various conjectures and questions are given.
We prove that there exists uncountably many pairwise disjoint open subsets of the Gelfand space of the measure algebra on any locally compact non-discrete abelian group which shows that this space is not separable (in fact, we prove this assertion for the ideal $M_{0}(G)$ consisting of measures with Fourier-Stieltjes transforms vanishing at infinity which is a stronger statement). As a corollary, we obtain that the spectras of elements in the algebra of measures cannot be recovered from the image of one countable subset of the Gelfand space under Gelfand transform, common for all elements in the algebra.
Let $e^{2πi\Q}$ denote the set of roots of unity. We consider subsets $E\subset e^{2πi\Q}$ that are quasi-independent or algebraically independent (as subsets of the discrete plane). A bijective map on $e^{2πi\Q}$ preserves the algebraically independent sets iff it preserves the quasi-independent sets, and those maps are characterized. The effect on the size of quasi-independent sets in the $n^{th}$ roots of unity $Z_n$ of increasing a prime factor of $n$ is studied.