content: isMatrix xs = null xs || all ((== (length.head $ xs)).length) xs
  
  isSquareMatrix xs = null xs || all ((== (length xs)).length) xs
  
  mult:: Num a => [[a]] -> [[a]] -> [[a]]
  mult uss vss = map ((\xs -> if null xs then [] else foldl1 (zipWith (+)) xs). zipWith (\vs u -> map (u*) vs) vss) uss
  
  gauss::[[Double]] -> [[Double]] -> [[Double]]
  gauss xs bs = map (map fromRational) $ solveGauss (toR xs) (toR bs)
      where toR = map $ map toRational
  
  solveGauss:: (Fractional a, Ord a) => [[a]] -> [[a]] -> [[a]]
  solveGauss xs bs | null xs || null bs || length xs /= length bs || (not $ isSquareMatrix xs) || (not $ isMatrix bs) = []
                   | otherwise = uncurry solveTriangle $ triangle xs bs
  
  solveTriangle::(Fractional a,Eq a) => [[a]] -> [[a]] -> [[a]]
  solveTriangle us _ | not.null.dropWhile ((/= 0).head) $ us = []
  solveTriangle ([c]:as) (b:bs) = go as bs [map (/c) b]
    where
    val us vs ws = let u = head us in map (/u) $ zipWith (-) vs (head $ mult [tail us] ws)
    go [] _ zs          = zs
    go _ [] zs          = zs
    go (x:xs) (y:ys) zs = go xs ys $ (val x y zs):zs
  
  triangle::(Num a, Ord a) => [[a]] -> [[a]] -> ([[a]],[[a]])
  triangle xs bs = triang ([],[]) (xs,bs)
      where
      triang ts (_,[]) = ts
      triang ts ([],_) = ts
      triang (os,ps) zs = triang (us:os,cs:ps).unzip $ [(fun tus vs, fun cs es) | (v:vs,es) <- zip uss css,let fun = zipWith (\x y -> v*x - u*y)]
          where ((us@(u:tus)):uss,cs:css) = bubble zs
  
  bubble::(Num a, Ord a) => ([[a]],[[a]]) -> ([[a]],[[a]])
  bubble (xs,bs) = (go xs, go bs)
      where
      idmax = snd.maximum.flip zip [0..].map (abs.head) $ xs
      go ys = let (us,vs) = splitAt idmax ys in vs ++ us
  
  main = do
    let a  = [[1.00, 0.00, 0.00,  0.00,  0.00,   0.00],
              [1.00, 0.63, 0.39,  0.25,  0.16,   0.10],
              [1.00, 1.26, 1.58,  1.98,  2.49,   3.13],
              [1.00, 1.88, 3.55,  6.70, 12.62,  23.80],
              [1.00, 2.51, 6.32, 15.88, 39.90, 100.28],
              [1.00, 3.14, 9.87, 31.01, 97.41, 306.02]]
    let b = [[-0.01], [0.61], [0.91], [0.99], [0.60], [0.02]]
    mapM_ print $ gauss a b
  