\DeclarePairedDelimiter with a name that is already defined [duplicate]

Question

How do I introduce a paired delimiter with \DeclarePairedDelimiter from mathtools, if the name that I want to use for the delimiter is already declared by some other package?

For example:

\documentclass{minimal}

\usepackage{mathtools}
\usepackage{physics}

\DeclarePairedDelimiter{\norm}{\lvert\lvert}{\rvert\rvert}

\begin{document}
I do not even need to use $\norm{v}$ to have an error.
\end{document}

Note that, unlike this question or this other question I am wondering about overriding an existing macro to make it a paired delimiter within the package mathttools, and not how to make a \newcommand with a name that has been already defined (in the latter case, I can, for example, \renewcommand).

Note that the question is not about how should you typeset a norm operator.

The reason why one may want to redefine a command in physics package as a mathtoolspaired delimiter is that a paired delimiter can open and close on two different lines.

Answer 1

As noted in my comment, one can undeclare a macro, such as \norm, with \let\norm\relax. And then, one can declare it as if it did not yet exist. The admonition is to be careful in redeclaring standard LaTeX (or package-defined) symbols, lest you break something else.

\documentclass{minimal}

\usepackage{mathtools}
\usepackage{physics}
\let\norm\relax
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}

\begin{document}
I do not even need to use $\norm{v}$ to have an error.
\end{document}

As campa notes, the use of \lVert and \rVert IS STRONGLY preferable to the use of \lvert\lvert and \rvert\rvert, as in

\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}

I have thus adopted that change in my answer.

Finally, Andrew notes that had \norm been defined via \DeclarePairedDelimiter, this simple method with \let would not work, since there is an associated macro also defined.