(Re-sending. Does this list drop mail from non-subscribers?) I've seen the hugs distribution that is hosted as http://ndmitchell.googlecode.com/files/MinHugs-Sep2006.exe and has the SHA1 checksum 02f62efe00334007eb7083d09bae6e692a48c7c2 evaluate the script below incorrectly on two different Windows XP computers. The correct output is [], but I get a non-empty list. On one computer I get different output for successive runs of the same script (restarting hugs) by saying "main". On the other one I get different output by saying "main" versus "ls". I can't reproduce the problem on two different UNIX-like systems with the September 2006 version of hugs. The problem goes away by replacing "Integer" with "Int". type Z = Integer qs :: Z -> Z qs 0 = 0 qs x = let (q,r) = divMod x 10 in r + qs q iqs :: Z -> Z iqs x = if x < 10 then x else iqs (qs x) ok :: Z -> Z -> Bool ok x y = iqs (iqs x * iqs y) == iqs (x*y) n :: Z n = 1000 ls :: [(Z,Z)] ls = [(x,y) | x<-[1..n], y<-[x..n], not (ok x y)] main = print ls