Q:

How to transform log(a)/2 into log(sqrt(a))?

I tried logcontract(log(a)/2) but it left the expression unchanged. How would I get Maxima to do that?

A:

Unfortunately there is no satisfactory way to accomplish that.
Maxima's simplification rules only work in one direction. Given an identity, e.g. f(a) = g(a), Maxima implements either f(a) --> g(a) or g(a) --> f(a). There isn't a way to switch from one to the other.
Given a rule f(a) --> g(a), it is possible to disable it, but it is clumsy. Let me know if you want to go down that road.

