Obviously, the code of Arc2 in ac.scm has been rewritten in some places, leading to optimisations in some cases but to slowdowns in other places. For example, (fib 10) is about 5 times (!) slower, but (fib 35) is about 30% faster. Maybe there are still easy optimisations possible.
btw, pg's code has been replaced by the older's code on the git, I'll fix that later on.
