# SP20:Lecture 4 prep

($1)$2 | $3 ($4) | $5 ($6)

I plan to talk about proof techniques and to start covering the definitions for functions. Last semester, proof techniques were covered in lecture 4 and lecture 5, while function properties were covered in lecture 5 and lecture 6. We'll see how far we get.

Please come to lecture knowing 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: Injective
A function is injective if, for all and , whenever , we have .
Definition: Surjective
A function is surjective if for every output , there exists an input such that .
Definition: Bijective