We prove the following theorem. Let X be a discrete field, and ξ\documentclass[12pt]{minimal}
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\begin{document}$$\xi $$\end{document} and η\documentclass[12pt]{minimal}
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\begin{document}$$\eta $$\end{document} be independent identically distributed random variables with values in X and distribution μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document}. The random variables S=ξ+η\documentclass[12pt]{minimal}
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\begin{document}$$S=\xi +\eta $$\end{document} and D=(ξ-η)2\documentclass[12pt]{minimal}
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\begin{document}$$D=(\xi -\eta )^2$$\end{document} are independent if and only if μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} is an idempotent distribution. A similar result is also proved in the case when ξ\documentclass[12pt]{minimal}
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\begin{document}$$\xi $$\end{document} and η\documentclass[12pt]{minimal}
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\begin{document}$$\eta $$\end{document} are independent identically distributed random variables with values in the field of p-adic numbers Qp\documentclass[12pt]{minimal}
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\begin{document}$${\mathbf {Q}}_p$$\end{document}, where p>2\documentclass[12pt]{minimal}
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\begin{document}$$p>2$$\end{document}, assuming that the distribution μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} has a continuous density.