Signed sumsets and restricted signed sumsets in groups and fields
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arXiv
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| Natura: | Preprint |
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2026
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| _version_ | 1866909014348005376 |
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| author | Mistri, Raj Kumar Prajapati, Nitesh |
| author_facet | Mistri, Raj Kumar Prajapati, Nitesh |
| contents | Let $A = \{a_1, \ldots, a_k\}$ be a nonempty finite subset of an additive abelian group $G$. For a nonnegative integer $h$, the \emph{$h$-fold signed sumset} of $A$, denoted by $h_{\pm} A$, is defined by $$ h_{\pm} A = \Biggl\{\sum_{i = 1}^{k} λ_i a_i : λ_i \in \{-h, \ldots, h\}, \ \sum_{i = 1}^{k} |λ_i| = h \Biggr\}, $$ and the \emph{restricted $h$-fold signed sumset}, denoted by $h_{\pm}^\wedge A$, is defined by $$ h_{\pm}^\wedge A = \Biggl\{\sum_{i = 1}^{k} λ_i a_i : λ_i \in \{-1, 0, 1\}, \ \sum_{i = 1}^{k} |λ_i| = h \Biggr\}. $$ We study direct and inverse problems for these signed sumsets, namely determining extremal bounds for their sizes and characterizing the structure of sets $A$ attaining these bounds. While such problems have been extensively studied and resolved in the additive group of integers, comparatively little is known in general abelian groups, especially for restricted signed sumsets. In this paper, we investigate the signed sumset $h_{\pm} A$ in arbitrary (not necessarily finite) abelian groups under the condition $A \cap (-A) \neq \varnothing$. We further analyze both $h_{\pm} A$ and $h_{\pm}^\wedge A$ when $A \cap (-A)$ has a prescribed size. These results are extended to generalized signed sumsets $H_{\pm} A = \bigcup_{h \in H} h_{\pm} A$, where $H$ is a finite set of nonnegative integers, with particular attention to $[0,h]_{\pm} A$. Furthermore, using the polynomial method, we establish nontrivial lower bounds for $|h_{\pm}^\wedge A|$ in arbitrary fields. In addition, for $h = 2, 3, 4$, we derive lower bounds for $|h_{\pm} A|$ in arbitrary fields under the condition $A \cap (-A) = \varnothing$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_03483 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Signed sumsets and restricted signed sumsets in groups and fields Mistri, Raj Kumar Prajapati, Nitesh Combinatorics Number Theory 11P70, 11B13, 11B75 Let $A = \{a_1, \ldots, a_k\}$ be a nonempty finite subset of an additive abelian group $G$. For a nonnegative integer $h$, the \emph{$h$-fold signed sumset} of $A$, denoted by $h_{\pm} A$, is defined by $$ h_{\pm} A = \Biggl\{\sum_{i = 1}^{k} λ_i a_i : λ_i \in \{-h, \ldots, h\}, \ \sum_{i = 1}^{k} |λ_i| = h \Biggr\}, $$ and the \emph{restricted $h$-fold signed sumset}, denoted by $h_{\pm}^\wedge A$, is defined by $$ h_{\pm}^\wedge A = \Biggl\{\sum_{i = 1}^{k} λ_i a_i : λ_i \in \{-1, 0, 1\}, \ \sum_{i = 1}^{k} |λ_i| = h \Biggr\}. $$ We study direct and inverse problems for these signed sumsets, namely determining extremal bounds for their sizes and characterizing the structure of sets $A$ attaining these bounds. While such problems have been extensively studied and resolved in the additive group of integers, comparatively little is known in general abelian groups, especially for restricted signed sumsets. In this paper, we investigate the signed sumset $h_{\pm} A$ in arbitrary (not necessarily finite) abelian groups under the condition $A \cap (-A) \neq \varnothing$. We further analyze both $h_{\pm} A$ and $h_{\pm}^\wedge A$ when $A \cap (-A)$ has a prescribed size. These results are extended to generalized signed sumsets $H_{\pm} A = \bigcup_{h \in H} h_{\pm} A$, where $H$ is a finite set of nonnegative integers, with particular attention to $[0,h]_{\pm} A$. Furthermore, using the polynomial method, we establish nontrivial lower bounds for $|h_{\pm}^\wedge A|$ in arbitrary fields. In addition, for $h = 2, 3, 4$, we derive lower bounds for $|h_{\pm} A|$ in arbitrary fields under the condition $A \cap (-A) = \varnothing$. |
| title | Signed sumsets and restricted signed sumsets in groups and fields |
| topic | Combinatorics Number Theory 11P70, 11B13, 11B75 |
| url | https://arxiv.org/abs/2605.03483 |