Bound Variable/Examples/Algebraic Example

Example of Bound Variable
In algebra:
 * $x^2 + 2 x y + y^2 = \paren {x + y}^2$

both $x$ and $y$ are bound variables.

This is illustrated in considering the full formal statement:
 * $\forall x : \forall y : \paren {x^2 + 2 x y + y^2 = \paren {x + y}^2}$

where each occurrence of $x$ and $y$ is bound by a quantifier.