text: """Don't start a paragraph with 'But'.
  
  ---
  layout:
  source: Justin Jungé
  source_url:
  title:
  date:       2016-03-10 12:31:19
  categories: writing
  ---
  
  Paragraphs should not start with certain bad words.
  
  """
  from proselint.tools import existence_check, memoize
  
  
  @memoize
  def check(text):
      """Do not start a paragraph with a 'But'."""
      err = "misc.but"
      msg = "No paragraph should start with a 'But'."
      regex = r"(^|([\n\r]+))(\s*)But"
  
      return existence_check(text, [regex], err, msg, ignore_case=False)
  