def rfc_persona_fisica
      consonants_n = CONSONANTS + ['Ñ']
      all_letters = consonants_n + VOWELS
      date = ::Time.at(rand * ::Time.now.to_f).strftime('%y%m%d')
      [
        fetch_sample(consonants_n),
        fetch_sample(VOWELS),
        fetch_sample(all_letters, count: 2).join,
        date,
        fetch_sample(HOMOCLAVE, count: 3).join
      ].join
    end
def rfc_persona_fisica
      consonants_n = CONSONANTS + ['Ñ']
      all_letters = consonants_n + VOWELS
      date = ::Time.at(rand * ::Time.now.to_f).strftime('%y%m%d')
      [
        fetch_sample(consonants_n),
        fetch_sample(VOWELS),
        fetch_sample(all_letters, count: 2).join,
        date,
        fetch_sample(HOMOCLAVE, count: 3).join
      ].join
    end
http://es.wikipedia.org/wiki/Registro_Federal_de_Contribuyentes_(M%C3%A9xico)
 Registro Federal de Contribuyentes (R.F.C.) para persona física