# Sidon sets for linear forms

Let $\varphi(x_1,\ldots, x_h) = c_1 x_1 + \cdots + c_h x_h$ be a linear form with coefficients in a field $F$, and let $V$ be a vector space over $F$. A nonempty subset $A$ of $V$ is a $\it \varphi-Sidon\ set$ if, for all $h$-tuples $(a_1,\ldots, a_h) \in A^h$ and $(a'_1,\ldots, a'_h) \in A^h$, the relation $\varphi(a_1,\ldots, a_h) = \varphi(a'_1,\ldots, a'_h)$ implies $(a_1,\ldots, a_h) = (a'_1,\ldots, a'_h)$. There exist infinite Sidon sets for the linear form $\varphi$ if and only if the set of coefficients of $\varphi$ has distinct subset sums. In a normed vector space with $\varphi$-Sidon sets, every infinite sequence of vectors is asymptotic to a $\varphi$-Sidon set of vectors. Results on $p$-adic perturbations of $\varphi$-Sidon sets of integers and bounds on the growth of $\varphi$-Sidon sets of integers are also obtained.

Mel Nathanson