Substituting expressions in Maxima result



Hi all,

I have a very long expression as a maxima result. In it there is quite
often the part sqrt(a^2 + b^2 + c^2) (the frobenius norm of a vector).
Now I want to substitute that by a variable like e.g. "myvectnorm".

Do I have to do that with a RegEx search/replace in an editor or can I
tell maxima to do that already inside maxima? I'd prefer doing it in
maxima to avoid stupid RegEx errors. And it would make for an easier
copying into C++ (which is tedious because all "^2" must be replaced).

Best regards,
weaker