```
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import qualified Data.Set as Set
newtype M = M { unM :: Int }
deriving (Show, Num, Integral, Enum, Real)
instance Eq M where
M a == M b = a `mod` 10 == b `mod` 10
instance Ord M where
M a `compare` M b = (a `mod` 10) `compare` (b `mod` 10)
f :: M -> Int
f = unM
g :: Int -> M
g 1 = M 10
g x = M x
main :: IO ()
main = do
let w = Set.fromList $ map M [1..10]
print w
let x = Set.map (* 10) w
print x
let y = Set.map (`div` 10) x
print y
let z = Set.map ((`div` 10) . (* 10)) w
print z
```

# omap for Set violates the laws

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