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

Ignore-this: 7fcc6a14cfb022d4a8318e89adf5cd7e

darcs-hash:20110210165128-3bd4e-263f526351a75ce3371f498b3976f42c3447f026.gz

asr/fotc,asr/fotc