propEqAfterDelete :: Keys -> Bool
propEqAfterDelete (Keys keys) =
  let keyMap = mapFromKeys keys
      k      = head keys
  in  HM.delete k keyMap == mapFromKeys (delete k keys)
propEqAfterDelete :: Keys -> Bool
propEqAfterDelete (Keys keys) =
  let keyMap = mapFromKeys keys
      k      = head keys
  in  HM.delete k keyMap == mapFromKeys (delete k keys)
propEqAfterDelete (Keys keys) =
  let keyMap = mapFromKeys keys
      k      = head keys
  in  HM.delete k keyMap == mapFromKeys (delete k keys)