Hi, Does anyone have ever used this option? I see no difference when I present this program to ghc with -fallow-overlapping-instances on/off: module Test where data T = T data F = F data OR a b = OR a b data AND a b = AND a b class C a b | a -> b instance C (OR T r) T instance C (OR r T) T instance C (AND F r) F instance C (AND r F) F -Kenny __________________________________________________ Do You Yahoo!? A free party for the most "shiok" photo! http://sg.yahoo.com/shiok