Marc:
I bit the bullet and did the optimal expt, you'll be amazed. It still is not tested extensively, but at least the code is straightforward. So now we have things like:
(##my-expt 8/27 1/3)
2/3
In the process, I discovered that ##exact-int.nth-root was buggy as hell and fixed it (and tested it). I trust it now.
The new routines begin with ##my-...
If other people want to test ##my-expt, that would help. Put it in a sibling directory to the lib directory in the gambc40b15 directory to compile it.
I removed srfi-56 and Alex Shinn from the CC list ;-).
Brad