Let $n$ be a fixed positive integer. A relation $R$ is defined in the set of integers $\mathbb{Z}$ such that $R = \{(x, y) : (x - y) \text{ is divisible by } n, x, y \in \mathbb{Z}\}$. Determine if $R$ is an equivalence relation.
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This relation is known as "congruence modulo $n$", written as $x \equiv y \pmod n$. It forms the foundational basis of modular arithmetic in number theory.