How can you tell if an algebraic relation is a function?

A function is a relation in witch each domain [x-value] has exactly one range [y-value].

For example:

[(3,2) (5,3) (2,6) (1,3)] Would be a function because no x-values repeat in the relation. It's inputs have one output.

[(3,2) (5,3) (5,6) (1,3)] Would not be a function because the x-values repeat in the function. The "5" inputs have two outputs.

Brainilest is appreciated.

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