That is ok, though I prefer to use => rather than = for evaluation result.
In texinfo I use @result{} which in HTML becomes ⇒ aks ⇒ aka
"rightwards double arrow". (Might be worth considering if you do a major re-formatting.)
I.e.
+ => "[c][b][a]"
All the other examples in that section use "=", so I followed that for consistency. The document as a whole is not consistent in that regard. If I do a major reformatting pass, I'll fix it throughout.
I'm not sure the "but" phrasing is an improvement: I think (without reversal) is semi-implied by "prepending", hence the parenthesis (i.e. a clarification), rather than using "but".
Okay, I've changed it back.
Thanks.