    # File lib/facets/core/string/unbracket.rb, line 16
      def unbracket(bra=nil, ket=nil)
        if bra
          ket = Sring.bra2ket[bra] unless ket
          ket = ket ? ket : bra
          s = self.dup
          s.gsub!(%r[^#{Regexp.escape(bra)}], '')
          s.gsub!(%r[#{Regexp.escape(ket)}$], '')
          return s
        else
          if m = String.bra2ket[ self[0,1] ]
            return self.slice(1...-1) if self[-1,1]  == m
          end
        end
        return self.dup  # if nothing else
      end