On Thu, Oct 19, 2006 at 04:03:38PM +0200, Mikael Johansson wrote: > isIdentity (PL xs) = all (\(i,j) -> i==j) (zip [1..] xs) > > isIdentity (PL xs) = xs == [1..(length xs)] How about a compromise? isIdentity (PL xs) = xs == zipWith const [1..] xs Best regards Tomasz