def replace_prepositive_abbr(txt, abbr)
      txt.gsub!(/(?<=\s#{abbr.strip})\.(?=\s)|(?<=^#{abbr.strip})\.(?=\s)/, '∯')
      txt.gsub!(/(?<=\s#{abbr.strip})\.(?=:\d+)|(?<=^#{abbr.strip})\.(?=:\d+)/, '∯')
      txt