Abbott, H. L., Sidon sets. Canad. Math. Bull. 33 (1990), no. 3, 335--341; the explicit constant $c<2/25$ in $\ell(N)>cN^{1/2}$, as [Gu04] and [BaRi26] cite it.

Alon, Noga and Erdős, P., An application of graph theory to additive number theory. European J. Combin. (1985), 201-203.

Bailleul, A. and Riblet, R., On the largest Sidon subset in a finite subset of $\mathbb{R}^N$. arXiv:2605.03181 (v1, 4 May 2026); Theorem 2.2 for sets of integers and Theorem 2.1 for finite subsets of $\mathbb{R}^N$. Linked from the problem's discussion thread in a comment of 28 May 2026, which cites the authors with wrong initials.

Guy, Richard K., Unsolved problems in number theory. 3rd ed., Problem Books in Mathematics, Springer, New York (2004), xviii+437 pp. Section C9 "Packing sums of pairs", pp. 177--178: "Let $a_1<a_2<\cdots<a_n$ be any sequence of integers. Is it true that it contains a Sidon subsequence $a_{i_1},\ldots,a_{i_m}$ with $m=(1+o(1))n^{1/2}$? Komlós, Sulyok & Szemerédi (see E11) proved this with $m>cn^{1/2}$", and Abbott's $g(m)>cm^{1/2}$ "for any constant $c<\frac{2}{25}$ and all sufficiently large $m$", where $g(m)$ is the largest $n$ such that every set of $m$ integers contains a Sidon subset of size $n$. Library home: Guy 2004.

Komlós, J. and Sulyok, M. and Szemerédi, E., Linear problems in combinatorial number theory. Acta Math. Acad. Sci. Hungar. 26 (1975), no. 1--2, 113--121, doi:10.1007/BF01895954. Library home: Komlós, Sulyok and Szemerédi 1975; result page Komlós, Sulyok and Szemerédi 1975, KSS theorem — translation-invariant comparison.

Riddell, J., On sets of numbers containing no $l$ terms in arithmetic progression. Nieuw Arch. Wisk. (3) (1969), 204-209.