const Map<int, String> numberToKanjiMap = {
  0: '冷',
  1: '一',
  2: '二',
  3: '三',
  4: '四',
  5: '五',
  6: '六',
  7: '七',
  8: '八',
  9: '九',
  10: '十',
  100: '百',
  1000: '千',
  10000: '万',
  100000000: '億',
  1000000000000: '兆',
};

const Map<int, String> extendedNumberToKanjiMap = {
  16: '京',
  20: '垓',
  24: '𥝱',
  28: '穣',
  32: '溝',
  36: '澗',
  40: '正',
  44: '載',
  48: '極',
};

const Map<int, String> numberToFormalKanjiMap = {
  0: '冷',
  1: '壱',
  2: '弐',
  3: '参',
  4: '肆',
  5: '伍',
  6: '陸',
  7: '漆',
  8: '捌',
  9: '玖',
  10: '拾',
  100: '陌',
  1000: '阡',
  10000: '萬',
};

const String yenSymbol = '円';
const String formalYenSymbol = '圓';

String numberToKanji(int number, {bool formal = false}) {
  throw UnimplementedError();
}

int kanjiToNumber(String kanji) {
  throw UnimplementedError();
}