Re: Overlapping, undecidable, incoherent -- or worse?

I don't know whether this was apparent, but only the instance pattern is used in determining which instance to use, so "PO a" is the same as "PO a" ... you need to make them different otherwise they don;t just overlap they are identical. the left-hand-side of the "=>" play no part in instance selection. That is why I suggested using new types. (infact it is your only option) Even priority would not help here, as the instances are identical. (there is a priority, in that if the instances are overlapping the most specific is used, IE choosing between (PO a) and (PO Int) PO Int wins is 'a' is an Int. Keean.