# File lib/journey/nfa/builder.rb, line 35
      def visit_OR node
        from  = @i += 1
        children = node.children.map { |c| visit c }
        to    = @i += 1

        children.each do |child|
          @tt[from, child.first]  = nil
          @tt[child.last, to]     = nil
        end

        @tt.accepting = to

        [from, to]
      end