I said: "leaves spmod and mod", but of course I cited a case where mod
fails, too (711871), and I just found another (831445) one where subres,
red, and mod fail (with algebraic:false). I have not re-checked all the
previous bugs with algebraic:true, but at least *some* of them fail with
gcd:subres, algebraic:true.
So spmod looks like the only viable choice. Or perhaps some other
algorithm with algebraic:true.
-s