User:Tnhung2011/mathfunc

$$ \begin{align} \text{pow}(x, n) &= (x\in\mathbb{N}^*\Rightarrow \prod_{i=1}^nx)\,\lor\,\frac{1}{x \times n} \\ \text{abs}(x) &= (x\in\mathbb{N}\Rightarrow x)\,\lor\,-x \\ \text{fact}(x) &= \prod_{i=1}^ni \end{align} $$