def yml_chapter(file, title, sections, numbered='false'):
    return ('- title: %s\n  file: %s\n  numbered: %s\n  sections: %s\n' % (title, file, numbered, sections))
def yml_chapter(file, title, sections, numbered='false'):
    return ('- title: %s\n  file: %s\n  numbered: %s\n  sections: %s\n' % (title, file, numbered, sections))