Reflexivity: For any $a \in \mathbb{Z}$, $a - a = 0$, which is a multiple of $n$ for any $n$. Thus, $a \sim a$.
Symmetry: If $a \sim b$, then $a - b = kn$ for some integer $k$. Then $b - a = -kn$, which is also a multiple of $n$. Thus, $b \sim a$.
Transitivity: If
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