How to reset \renewcommand\l{\lambda} locally

Question

I have a large document with a lot of equation, the author overwritten the original \l (used to get polish letter ł) with \renewcommand\l{{\lambda}}. It would be to much work to find all the \l in all the equations and change it to \lambda. I only need couple of ł it the entire doc so I need to reset locally the \l command. How do I do that? \renewcommand\l{???}

Answer 1

You cannot reset a \renewcommand. But there are several options.

The cleanest would be to write ł instead of \l directly. This merely requires saving the document as UTF-8 and either using a modern LaTeX processor (LuaTeX or XeLaTeX) or to include the inputenc package with the utf8 option (\usepackage[utf8]{inputenc}).

Alternatively, you can define a new command to include \l immediately before it’s redefined:

\let\lw\l
\renewcommand\l{{\lambda}}

… and then just use \lw in place of \l to typeset ł.

Or you could change the redefinition of \l so that it only includes the λ in math mode, and includes ł in text mode. But I wouldn’t do that – it’s very unintuitive and hard to understand as a reader of the source code. Still, here it is:

\let\oldl\l
\renewcommand\l{\relax\iffmode\lambda\else\oldl\fi}

% … usage:

Here’s a z\l oty for your effort. $\l = 1\ \mL$

… which will render as:

Here’s a złoty for your effort. λ = 1 µL