Let n be a positive integer and
$\underline {n}=\{1,2,\ldots ,n\}$. A conjecture arising from certain polynomial near-ring codes states that if
$k\geq 1$ and
$a_{1},a_{2},\ldots ,a_{k}$ are distinct positive integers, then the symmetric difference
$a_{1}\underline {n}\mathbin {\Delta }a_{2}\underline {n}\mathbin {\Delta }\cdots \mathbin {\Delta }a_{k}\underline {n}$ contains at least n elements. Here,
$a_{i}\underline {n}=\{a_{i},2a_{i},\ldots ,na_{i}\}$ for each i. We prove this conjecture for arbitrary n and for
$k=1,2,3$.