Definition:Heaviside Step Function/Two Variables

Definition
Let $u: \R \to \R$ be the Heaviside step function.

Then the Heaviside step function of two variables is the real function $u : \R^2 \to \R$ defined as the product of two step functions of one variable:


 * $\map u {x, y} := \map u x \map u y$

In other words:


 * $\map u {x, y} := \begin{cases}

1 & : \paren {x > 0} \land \paren {y > 0} \\ 0 & : \text {otherwise} \end{cases}$