# SP20:Lecture 4 prep

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Please come to lecture with the following definitions:

Definition: Function
If and are sets, then a function from to (written ) is an unambiguous rule giving, for every input , an output . is called the domain of ; is called the codomain.
Definition: Surjective
A function is surjective if for every output , there exists an input such that .
Definition: Injective
A function is injective if, for all and , whenever , we have .
Definition: Bijective