An involution is a function $f: A \rightarrow A$ where $f(f(x))=x$.
A fixed point of any function $f: A \rightarrow A$ is an element $x \in A$ for which $f(x)$ $=x$.
Which of the following statement(s) must be true for any involution $f: \mathrm{A} \rightarrow \mathrm{A}?$
- The number of fixed points of an involution $f$ is even if the number of elements in $\mathrm{A}$ is odd.
- The number of fixed points of an involution $f$ is even if the number of elements in $\mathrm{A}$ is even.
- Every bijective function $f: \mathrm{A} \rightarrow \mathrm{A}$ is an involution.
- Every involution $f: \mathrm{A} \rightarrow \mathrm{A}$ is a bijective function.
