Added 0<x-y→0<Sx-y (by Ana Bove).
Added 0<x-y→0<Sx-y (by Ana Bove).

Ignore-this: 6e406e1ce4c0d33e9be8a4ee81910d6a

darcs-hash:20110210165514-3bd4e-82e7cce1ed8696fc29322de36d0c19097985514d.gz

asr/fotc,asr/fotc