def capturing_decidable?
      @capturing_decidable ||=
        children.all? {|_| _.capturing_decidable? } and
        ( children.all? {|_| _.capturing? } or
          children.none? {|_| _.capturing? } )
    end
def capturing_decidable?
      @capturing_decidable ||=
        children.all? {|_| _.capturing_decidable? } and
        ( children.all? {|_| _.capturing? } or
          children.none? {|_| _.capturing? } )
    end
(see Parser#capturing_decidable?)