# File truthtable/qm.rb, line 124
    def qm(tbl)
      return [] if tbl.empty?
      tbl = intern_tbl(tbl)
      prime_implicants = find_prime_implicants(tbl)
      essential_prime_implicants, chart = make_chart(prime_implicants, tbl)
      additional_prime_implicants = search_minimal_combination(chart)
      (essential_prime_implicants.keys + additional_prime_implicants).sort.reverse.map {|t|
        extern_term(t)
      }
    end