   def member?(collection, value)
 
   @doc """
-  Retrieve the collection' size.
+  Retrieves the collection's size.
   """
   @spec count(t) :: non_neg_integer
   def count(collection)

  @type continuation :: (acc -> result)

  @doc """
  The reduce function.

  Most of the operations in `Enum` are implemented in terms of reduce.
  This function shuold simply apply the given `reducer` function to each
  item in the collection and proceed as expected by the returned accumulator.

  As an example, here is the implementation of `reduce` for lists:

  def reduce(collection, acc, fun)

  @doc """
  Checks if a value exists within the collection.

  Membership should be tested with the match (`===`) operator.
  """
