class Kramdown::Converter::Html

def convert_footnote(el, _indent)
  repeat = ''
  if (footnote = @footnotes_by_name[el.options[:name]])
    number = footnote[2]
    repeat = ":#{footnote[3] += 1}"
  else
    number = @footnote_counter
    @footnote_counter += 1
    @footnotes << [el.options[:name], el.value, number, 0]
    @footnotes_by_name[el.options[:name]] = @footnotes.last
  end
  "<sup id=\"fnref:#{el.options[:name]}#{repeat}\">" \
    "<a href=\"#fn:#{el.options[:name]}\" class=\"footnote\">#{number}</a></sup>"
end