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**Formal Definition**

A **relation** between sets $A$ and $B$ is a subset $\Re$ of $A \times B$.We read $(a,b)\in \Re$ as "$a$ is related to $b$" and write $a\Re b$.

**Informal Definition**

Replace this text with an informal definition.

**Example(s)**

The graph of the function $f$ where $f(x)=x$^{3} for all $x\in \Re$,is the subset $\{(x,x^3)|x\in \mathbb{R}\}$ of $\mathbb{R}\times\mathbb{R}$.Thus it is a relation on $\mathbb{R}$.

**Non-example(s)**

The graph of the function $f$ where $f(x)=x$^{2} for all $x\in \Re$,is the subset $\{(x,x^2)|x\in \mathbb{R}\}$ of $\mathbb{R}\times\mathbb{R}^+$.Thus it is not a relation on $\mathbb{R}$ because it doesn't graph the $\mathbb{R}^-$.

**Additional Comments**

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