How to use \varepsilon as default

Question

I am writing a document, and I used \epsilon throughout. I would really like to change it to \varepsilon, but manually it would be quite a struggle.

So the question is whether I can put something in the preamble so that \epsilon actually give the same output as \varepsilon.

I tried with \newcommand{\epsilon}{\varepsilon}, but it didn't work (I imagine because \epsilon is an already defined command). How can I solve this problem?

Answer 1

Indeed, \epsilon is already defined.

In this case it's safe to do

\renewcommand{\epsilon}{\varepsilon}

^{I know that \let\epsilon\varepsilon would be slightly more efficient, but it's not for beginners.}

Note that in this way you have no way to recover the original \epsilon symbol, but that should not be a problem. In case you need the original, you need to save its meaning, so you can do

\let\uglyepsilon\epsilon
\let\epsilon\varepsilon

(choose a different name than \uglyepsilon, if you so prefer). Now using \epsilon or \varepsilon in the document will produce ε, while \uglyepsilon will produce ϵ. For this purpose, \let is needed.