LaTeX_dynamic

Programming in $\LaTeX3$. Motivated by

1. Fixed template of function definition: $$ N: \left{\begin{array}{ccc} H&\to&\mathbb{R}^+\ x&\mapsto&\lVert x\rVert\

    \end{array}\right.
   

$$

 \begin{equation*}
        N: \left\{\begin{array}{ccc}
            H&\to&\mathbb{R}^+\\
            x&\mapsto&\norm{x}\\
            
        \end{array}\right.
    \end{equation*}

we may abstract a environment or function to gain generality.

2. Optional argument in \newcommand or \def

\newcommand{\norm}[1]{\left\Vert #1 \right\Vert}

but with various kinds of norms, $\lVert f\rVert_{C^k(\overline{\Omega})}$, $\lVert f\rVert_{W^{n,p}}$, $\lVert x\rVert_{\mathcal{L}(E,F)}$, it would be more propre to add an optional argument to present the subscription as \norm[]{}.

3. Calculation and control flow in $\LaTeX_{2\varepsilon}$