(Logic) can a set be both reflexive and asymmetric?

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I am just starting to learn logic at undergraduate level.

My exercise book is asking me to: "Specify a relation and a set $S$ such that the relation is reflexive on $S$ and asymmetric".

How can a set be both reflexive and asymmetric?

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Suppose $S$ is non-empty. Take an element $a\in S$; since the relation is reflexive $a\sim a$. Yet since the relation is asymmetric, this implies $a\not\sim a$, which is absurd.

We get around this by specifying $S=\varnothing$ and the relation as the empty relation. It is vacuously reflexive and asymmetric.