\begin{definition}[Definition:Many-to-One Relation]
A relation $\RR \subseteq S \times T$ is '''many-to-one''' {{iff}}:
:$\forall x \in \Dom \RR: \forall y_1, y_2 \in \Cdm \RR: \tuple {x, y_1} \in \RR \land \tuple {x, y_2} \in \RR \implies y_1 = y_2$
That is, every element of the domain of $\RR$ relates to no more than one element of its codomain.
{{transclude:Definition:Many-to-One Relation/Defined
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  | title    = Defined
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\end{definition}