content: -- vectorized boolean operations defined in terms of step or cond
  
  import Numeric.LinearAlgebra
  
  infix  4  .==., ./=., .<., .<=., .>=., .>.
  infixr 3  .&&.
  infixr 2  .||.
  
  a .<.  b = step (b-a)
  a .<=. b = cond a b 1 1 0
  a .==. b = cond a b 0 1 0
  a ./=. b = cond a b 1 0 1
  a .>=. b = cond a b 0 1 1
  a .>.  b = step (a-b)
  
  a .&&. b  = step (a*b)
  a .||. b  = step (a+b)
  no a      = 1-a
  xor a b   = a ./=. b
  equiv a b = a .==. b
  imp a b   = no a .||. b
  
  taut x = minElement x == 1
  
  minEvery a b = cond a b a a b
  maxEvery a b = cond a b b b a
  
  -- examples
  
  clip a b x = cond y b y y b where y = cond x a a x x
  
  disp = putStr . dispf 3
  
  eye n = ident n :: Matrix Double
  row = asRow . fromList    :: [Double] -> Matrix Double
  col = asColumn . fromList :: [Double] -> Matrix Double
  
  m = (3><4) [1..] :: Matrix Double
  
  p = row [0,0,1,1]
  q = row [0,1,0,1]
  
  main = do
      print $ find (>6) m
      disp $ assoc (6,8) 7 $ zip (find (/=0) (eye 5)) [10..]
      disp $ accum (eye 5) (+) [((0,2),3), ((3,1),7), ((1,1),1)]
      disp $ m .>=. 10  .||.  m .<. 4
      (disp . fromColumns . map flatten) [p, q, p.&&.q, p .||.q, p `xor` q, p `equiv` q, p `imp` q]
      print $ taut $ (p `imp` q ) `equiv` (no q `imp` no p)
      print $ taut $ (xor p q) `equiv` (p .&&. no q .||. no p .&&. q)
      disp $ clip 3 8 m
      disp $ col [1..7] .<=. row [1..5]
      disp $ cond (col [1..3]) (row [1..4]) m 50 (3*m)
  
  