# File lib/journey/nfa/builder.rb, line 21
      def visit_GROUP node
        from  = @i += 1
        left  = visit node.left
        to    = @i += 1

        @tt.accepting = to

        @tt[from, left.first] = nil
        @tt[left.last, to] = nil
        @tt[from, to] = nil

        [from, to]
      end