max expr size  =    4
  |- on ineqs  =    3
  |- on conds  =    3
max  #-tests   =  500
min  #-tests   =   25  (to consider p ==> q true)
max  #-vars    =    2  (for inequational and conditional laws)

_ :: Int  (holes: Int)
_ :: [Int]  (holes: [Int])
_ :: Int -> [Int]  (holes: Int -> [Int])
return :: Int -> [Int]
(>>=) :: [Int] -> (Int -> [Int]) -> [Int]
(>=>) :: (Int -> [Int]) -> (Int -> [Int]) -> Int -> [Int]

(xs >>= return) == xs
            f x == (return x >>= f)
    (f >=> g) x == (f x >>= g)
 (f >=> return) == f
 (return >=> f) == f