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
0 :: Int
1 :: Int
id :: Int -> Int
(+) :: Int -> Int -> Int
negate :: Int -> Int
(-) :: Int -> Int -> Int

             id x == x
negate (negate x) == x
            x + 0 == x
     x + negate x == 0
            x + y == y + x
            x - y == x + negate y

    x <= x + 1
x - 1 <= x