 
   @doc """
   Puts the given `value` under `key` unless the entry `key`
-  already exists.
+  already exists in `map`.
 
   ## Examples
 

  end

  @doc """
  Returns whether a given `key` exists in the given `map`.

  ## Examples


  defdelegate merge(map1, map2), to: :maps

  @doc """
  Merges two maps into one, resolving conflicts through the given `callback`.

  All keys in `map2` will be added to `map1`. The given function will be invoked
  when there are duplicate keys; its arguments are `key` (the duplicate key),
  `value1` (the value of `key` in `map1`), and `value2` (the value of `key` in
  `map2`). The value returned by `callback` is used as the value under `key` in
  the resulting map.

  ## Examples

