Let $\exp$ be the D1932: Standard natural real exponential function.
Let $e$ be the D169: Napier's constant.
Let $x \in \mathbb{R}$ be a D993: Real number.

Then \begin{equation} \exp(x) = e^x \end{equation}

Let $x \in \mathbb{R}$ be a D993: Real number.

Then \begin{equation} \sum_{n = 0}^{\infty} \frac{x^n}{n!} = \left( \sum_{n = 0}^{\infty} \frac{1}{n!} \right)^x \end{equation}