old_contents: # -*- coding: utf-8 -*-
  
  def add(new, previous=None):
      if previous is None:
          return new
      return previous + new
  
  
  def collect(new, previous=None):
      if previous is None:
          return [new]
      return previous + [new]
  
  
  def merge(new, previous=None):
      return add(new, previous)
  
new_contents: # -*- coding: utf-8 -*-
  
  def add(next_, previous=None):
      if previous is None:
          return next_
      return previous + next_
  
  
  def collect(next_, previous=None):
      if previous is None:
          return [next_]
      return previous + [next_]
  
  
  def merge(next_, previous=None):
      return add(next_, previous)
  
subject: Rename misleading new to next