[TDF] Add convenience overload for Reduce.
[TDF] Add convenience overload for Reduce.

Reduce(Op, 0) is nicer than Reduce(Op, "", 0).

karies/root,zzxuanyuan/root,karies/root,karies/root,simonpf/root,zzxuanyuan/root,karies/root,karies/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,simonpf/root,simonpf/root,root-mirror/root,olifre/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,zzxuanyuan/root,karies/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,olifre/root,karies/root,olifre/root,olifre/root,zzxuanyuan/root,root-mirror/root,simonpf/root,karies/root,simonpf/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,simonpf/root,zzxuanyuan/root,olifre/root,zzxuanyuan/root,simonpf/root,simonpf/root,zzxuanyuan/root,root-mirror/root,zzxuanyuan/root,simonpf/root,zzxuanyuan/root,simonpf/root,root-mirror/root,root-mirror/root,simonpf/root,karies/root,olifre/root,karies/root