Hakuin’s system of practice and its background

ABSTRACTBased on the works of Hakuin Ekaku 白隱慧鶴 (1686–1769), this article analyses the practice system he constructed and its background and clarifies the following two conclusions. First, the system of practice demonstrated by Hakuin involves focus on one specific kind of practice to achieve ‘seeing one’s nature’ (kenshō 見性), and then ‘practice after insight’ (gogo no shugyō 悟後の修行). Among them, ‘practice after insight’ consists of two parts: ‘seeking bodhi above’ (jōgu bodai 上求菩提) by constantly consulting kōan cases to refine one’s own realisation, and ‘cultivating sentient beings below’ (geke shujō 下化眾生) by guiding other people through giving dharma teachings. Second, the core of Hakuin’s practice system is the three essential elements consisting of ‘insight,’ ‘seeking bodhi above,’ and ‘cultivating sentient beings below.’ The background against which they formed was the three enlightenments obtained in Hakuin Ekaku’s life.KEYWORDS: Hakuinseeing one’s natureseeking bodhi abovecultivating sentient beings belowgiving dharma teachings Disclosure statementNo potential conflict of interest was reported by the author(s).Notes1. Yoshizawa Katsuhiro summarised and analysed past research on Hakuin and suggested several topics that could be studied in the future. See Yoshizawa, ‘Hakuin kenkyū no genjō to kadai’.2. There are also various views in the school regarding the method of grasping Hakuin Zen’s kōan system. For details, see Yanagi, ‘Hakuin no jissen taikei to sono haikei’, 318–320.3. Yanagida, Nihon no Bukkyō 9.4. Ibid., 260–261.5. Ibid., 256.6. Yanagida and Mohr, ‘Taidan Hakuin no zen’.7. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’.8. Shibayama, ‘Hakuin Zen no kanna ni tsuite’.9. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’, 100.10. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’, 90.11. Yoshizawa, Hakuin Zenga wo yomu, 196.12. Yoshizawa, ‘Bodaishin nakereba madō ni otsu’; Hanazono Daigaku Kokusai Zengaku Kenkyūjo, Hakuin zenga bokuseki, 121.13. Yoshizawa, Hakuin: Zenga no sekai, 262; idem, Hakuin Zenji no fushigi na sekai, 39; idem, Hakuin Zenga wo yomu, 129–130.14. Obama, ‘Hakuin no shugyōkan’, 44.15. Yoshizawa (‘Bodaishin nakereba madō ni otsu’) criticises Yanagida, Nihon no Bukkyō 9, but does not mention the statement by Maryū. Although Obama introduced Maryū’s account, she did not discuss how it had anything to do with her own account (see Obama, Hakuin no shugyōkan, 96).16. I have analyzed the practice system of Hakuin and the relationship between the practice system and spiritual experience in two previous articles, but each of which is limited to a brief discussion. See Yanagi, ‘Hakuin Ekaku to Sugyōroku’; idem, ‘Hakuin no kotoba wo yomu’. In contrast, this article tries to show the basis for my opinion in detail by quoting relevant quotations from Hakuin. In addition, this study was based on the results of Yoshizawa’s research on Hakuin, as I cited the translations and writings of Yoshizawa in this article. Here, I pay respect and show gratitude to Yoshizawa, who has substantially advanced the study on Hakuin.17. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’, 88.18. H12.180: 禪定誦經、念佛持戒、皆是見性の助因なるべし.19. H9.447–50: 或 ハ 定坐 シ、或 ハ 誦經 シ、或 ハ 諷呪 シ、或 ハ 念佛 シ、……行持 ハ 縱 イ 品 ナ 異 ナレドモ、ソノ 所證 ニ 到 ツテハ、豈兩般有 ンヤ.20. H9.461–63: 參禪 モ 念佛 モ 及 ビ 看經誦經 ヲサヘニ、盡是 レ 見道 ノ 輔助 ニシテ 行路 ノ 人 ノ 杖 ノ 如 クナル 事 ヲ。……只肝心 ハ 杖子 ヲ 擇 バズ 行裝 ヲ 論 ゼズ、一氣 ニ 進 ンデ 退 ゾカズ、速 カニ 京師 ニ 到 ルヲ 以 テ 賢 ナリトス.21. H9.447.22. H13.32–39.23. However, what Hakuin acknowledged was the pure and unadulterated engagement in kōans, not all forms of zazen. See Yanagi, ‘Hakuin zenji ni okeru zazen to kōan’.24. H9.488–89. Nishi Yoshio 西義雄 pointed out that Hakuin reduced the various practices inside and outside of Buddhism to that of seeing one’s nature. See Nishi, ‘Hakuin zenji ni yoru Nihon no seishin bunka tōitsu to sono keiki’.25. H9.359–60: 一心不亂、純一無雜 ノ 田地 ニ 至 ラシメン 方便.26. H9.489–94.27. Gaofeng Yuanmiao’s three essentials are found in ‘Hangzhou Xi Tianmushan Shizi chansi fayu’ 杭州西天目山師子禪寺法語 [Buddhist Sayings of the Shizi Chan Monastery of the Xitian Mu Mountain in Hanzhou], Gaofeng dashi yulu, Z no. 122: 1.673a–b; and ‘Shizhong’ 示眾 [Preaching to the Public], Gaofeng Heshang chanyao, Z no. 122: 714a–b. Hakuin collected what he wrote in his own writings, such as Yae Mugura 八重葎 [Goosegrass], fascicle 3, H7.110; Itsu made gusa 壁生草 [Sedum], fascicle 2, H3.248; Kanzanshi Sendai Kimo 寒山詩闡提記聞 [Records of the Icchantikas of Han Shanshi], fascicle 3, O4.283; and Sokkōroku Kaien Fusetsu 息耕錄開筵席普說 [Preaching the Xigeng Lu during Banquets], O2.412–13.28. O2.412.29. H2.165.30. H9.211.31. Yanagida elaborated on Hakuin’s emphasis on the mu character kōan as follows: ‘The reason why Hakuin took the character mu (later a hand) as the only kōan was because he considered it the most ideal way to see one’s nature based on his own experience,’ ‘Japanese Zen Buddhism officially proposed this kōan around the time of Hakuin. The Hekiganroku did not include this kōan, and Japan’s medieval Zen Buddhism, which took the Hekiganroku as the most important book of the school, did not show concern for this kōan. The kana hōgō (dharma talks in Kana Script) of the Shinchi Kakushin 心地覺心 who brought the the Wumen guan clearly speaks of the mu character kōan, but it is not particularly emphasised. In addition, the Daitō ippyakunijussoku 大燈一百二十則 [Daito’s One Hundred and Twenty Kōans] includes this kōan in the sixth case, and there are also references to it in the Missancho [Records of secret instruction on kōan] made in the Middle Ages, but not as the only absolute kōan as described in the Wumen guan. See Yanagida, Rinzai no kafū, 248–245.32. H7.201.33. Tokiwa, ‘Hakuin Ekaku no Sekishu onjō wo Oradegama to Tōzan Goiju toni kiku’.34. H3.191; H12.63, etc.35. H3.190; 5.143; 7.218, 225–26, 240, etc.36. H12.45: 前の指南と拔群の相違ありて、誰に[々]も(格別に)疑團起り易く、工夫(勵み)進み易き事、雲泥の隔有之樣に覺へ侍り。是に依りて、唯今專一に隻手の工夫を勸め侍り.37. H8.163: 老僧、隻手の小關有り、人を出だすこと大凡そ數を記せず.38. H2.288–90: 五日三日乃至七日 ノ 中 ニハ、必定決定聞 キトヾケ 玉 ウベキゾ.39. As far as I know, Hakuin does not elaborate how the ‘one hand sound’ can more ‘easily arouse great doubts’ than previous kōans such as the mu character (H12.45). I speculate that it is because of the following reasons. Although the mu character kōan was praised as a good way to ‘easily arouse great doubts’ (H9.494) and was used to guide people by Hakuin, it still leaves room for a discriminating mind because of using language. This was recognised at the beginning of the founding of kōan exercise. In a letter to literati, Dahui Zonggao 大慧宗杲 (1089–1163), who perfected the method of kōan exercise, cautioned in advance that ‘you should not have an understanding of nothingness, nor a logical understanding’ (不得作有無會, 不得作道理會); see ‘Da Fu Shumi (Jishen) (i.e., Fu Zhirou 富直柔 (1084–1156)’ 答富樞密 (季申), Dahui Pujue chanshi yulu, T no. 1998A, 47: 26.921c. The Wumen guan (1229), which Hakuin used to instruct monks, also states that mu character must not be understood as either nothingness or existence and nonexistence (K1.223–24, Wumen guan, comment on the first case [第一則評唱] T no. 48.293a). Thus, the mu character was capable of a certain amount of intellectual thought, such as ‘it is the nothingness’ (虛無會) or ‘it is the nonexistence’ (有無會). In contrast, the kōan of ‘one hand sound,’ in which the practitioner is asked without question to ‘listen to the sound of one hand’ by thrusting out one hand with a jerk, is difficult to understand intellectually. In this way, the reference to the mu character kōan will revolve around some intellectual thinking such as the ‘mu of nothingness’ and the ‘mu of nonexistence.’ In contrast, the kōan of ‘one hand sound’, which forces the practitioner to listen to the sound of a single hand without asking and answering, would be difficult to add to such an intellectual understanding. Therefore, the practitioner will not take a futile detour through further unnecessary assumptions, and it would be easier to have the great doubt appear. In addition, Hakuin painted pictures of the monk Hotē 布袋 with one hand stretched out, or even just a picture of a hand stretched out, with the words ‘listen to the one hand sound’ (どうぞして隻手の聲を聞く様にしやれよ), ‘if you don’t listen to the one hand sound, it’s all nonsense’ (かた手の聲をきかねば、みなたわ事の皮だぞよ) and so on. See Hanazono Daigaku Kokusai Zengaku Kenkyūjo, Hakuin zenga bokuseki, Zengahen, 240–245, 485. Cutting off all distinctions, stretching out a hand in front of one’s eyes, casting aside language and concepts, and visually approaching the practitioner are also very compatible with the Zen paintings that Hakuin used in teaching the dharma in order to cultivate the sentient beings below.40. H12.34: 自性本有之樣, 一囘分明見得.41. H9.353: 眾生 ニ 在 リテモ 穢 レズ 減 ラズ、佛 ニ 在 リテモ 淨 カラズ 増 サズ.42. O4.247: 未爲見性, 而爲見思雲霧所蓋覆, 貪瞋家賊所劫奪.43. H9.490–92.44. H7.217–18.45. Yoshizawa, ‘Bodaishin nakereba madō ni otsu’, 121.46. H7.223–26.47. K2.1086.48. O6.329.49. K2.1086: 下化法施爲第一.50. H5.151.51. H11.134: 同 ジク 種智 ヲ 圓 カニスル 故 ニ.52. H6.608: 法施の功徳は塵劫を歴るとも盡る事なし。現當二世の利益にして、菩薩の威儀にも叶ひ、佛國土の因縁共成るぞかし.53. H13.39: 若人法施を行ぜんと欲せば、先すべからく三經五論、普く内典外典に入り、傳記百家の書を搜索して、廣く大法財を聚むべし。……法財無くんば、何を以てか法施を行ぜん.廣ろく内典外典を探ぐり、無量の法財集めておいて、三つの根機を救わにやならぬ.54. K2.1151–52.55. O6.328–29.56. O7.116.57. H4.235-236: 疎山の壽塔、牛窓櫺、鹽官の扇子、乾峰の三種、是等の大事を了畢すれば、智眼次第に圓明にして能く人の利鈍を辨じ、賢愚を見る.58. O6.324: 差別の智、明了ならざれば、眾生の機に應じて利益することあたはず.59. H7.271–72: 眞正の智見を具せず、人の根機を辨ずる事能わずんば、妄りに説法する事なかれ.60. Hekiganshū hishō 碧巖集秘抄 [Secret Commentary on the Hekiganroku (Biyan Lu)], 415: 四弘誓願 ニ 依 ッテ 爲人度生 スレバ、覺 ヘズ 自分 モ 四智圓明 ニ 進 ミ 行 ク.61. Hanazono Daigaku Kokusai Zengaku Kenkyūjo, Hakuin zenga bokuseki, 265; Yoshizawa, Hakuin zenga wo yomu, 16, 130.62. H12.65: 大凡、十方の賢聖、古今の智者、法成就に到らんがために、常に願輪に鞭うつ。此故に普賢に七十の願あり、彌陀に四十の願あり。何れも上求菩提の爲めに下化眾生の大法施を行ず.63. H2.206.64. Yanagi, ‘Hakuin Ekaku to Bodaishin no han’, 311–10.65. H3.250–51.66. H3.194–97.67. Hakuin does not elaborate on ‘seeking bodhi above’ nor mention where it begins. I think there are two possibilities, namely (1) it begins right after seeing one’s nature, or (2) it begins after reaching a specific realisation through consulting multiple kōans after seeing one’s nature. In this article, I consider that (1) right after seeing one’s nature, he began to ‘seek bodhi above’, and I have compiled this into Figure 1, for two reasons: first, Hakuin said that the practice after insight consists of two things: seeking bodhi above and cultivating sentient beings below, and then presented a series of processes consisting of ‘seeing one’s nature → engaging in countless kōans → teaching the dharma’ (H3.32-39; 7.223-226; K2.1086); Second, as Yoshizawa points out, the picture of ‘Dragon Staff Horsetail Whisk’ bestowed immediately after seeing one’s nature depicts the Dragon Staff and Horsetail Whisk symbolising seeking bodhi above and cultivating sentient beings below respectively. But the possibility of (2) cannot be denied.68. K2.1141–42, 1083–86. In the Hōkan ishō, there are two places in which the explanations of the four wisdoms can be seen (K2.1083–86, 1141–42), and there are some differences. Two major differences are notable. First, the first half of the text placed the gathering of dharma assets in the third stage, while the second half placed it in the fourth stage. Second, as for the fourth stage, the first half only contains the teaching of the dharma (the cultivation of sentient beings below), while the second half also contain seeking bodhi above. From this, it can be seen that this difference may be insignificant to Hakuin, and he does not care much about building a refined system of practice. Yoshizawa points out that the Hōkan ishō was written in order to hasten the publication of the Gudō roku, and its original manuscript was later supplemented (K2.1216–17). The two different descriptions in the Hōkan ishō maybe the result of combining different texts at different times.69. K1.609.70. K2.1086.71. K2.1142.72. O7.216: 親入正中來一位,依兼中至眞修,獲得妙觀察智、成所作智等四智.73. Yanagida, Nihon no Bukkyō 9, 260–61.74. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’, 90.75. Yoshizawa, Hakuin zenga wo yomu, 196.76. Obama, ‘Hakuin no shugyōkan’, 44.77. Maryū, ‘Hakuin Zen niokeru ningen Keisei no shisō’, 100.78. Ibid., 88.79. Ibid., 89–90.80. O6.324: 何をか大圓鏡智と云。所謂初心の學者、……本來具足の佛性を見徹せんことを要とし.81. Ibid., 326–27: 一旦見道分明なれども、觀照の力強大ならざるが故に、……此の悟後の修行なければ、見性の者多は差過する處なり. 故に平等性智とは前の大圓鏡智に止らず、益 々 進で、悟後の修行を專らとす. ……見性了 々 分明にして、掌上を見るが如く、……一切の境界に於て、全體照破して、其の心退轉せざれば、……眞實平等の境界を成ずるを得て、平等性智と名く.82. Ibid., 328–29: 妙觀察智と云は、……利益眾生の方便に通達するを旨とす。……先づ佛祖の言教を以て日夜參究すべし. 五家七宗の玄賾、五時八教の妙義一 々 決擇して、餘力あらば、諸子百家異道の深理を明むべし. ……唯幾重 々々 も佛祖の關鎖を透て、方便自在に普く眾生の機に應ずるを妙觀察智と名く.83. Ibid., 330: 成所作智とは、是究竟解脱の境界にして、祕密總持門也。是を無垢智と云ひ、又無作の徳と云。是の智を成せざれば、自利 々 他の所作に於て大自在を得ざるが故に. ……みな有功用の智とす. 此の智は修證學得の分際を超て、指南言詮の及ばざる處なり.84. Obama, Hakuin no shugyōkan, 14.85. K1.606; N29686. N398.87. K2.1083–86.88. K2.1141–1142.89. K1.606: 煥發偏正囘互祕奥, 如見掌上。疑兕乍斃, 不堪歡喜.90. H3.233.91. N568; N691.92. H9.422, N15–16.93. H3.153; H7.127.94. H7.131.95. H3.155–58.96. H3.162.97. Hakuin mentions what realized in the mu kōan, but it is not clear who granted this mu kōan to him, or whether he contemplated it according to his own judgment. Maybe he casually came to see the mu character kōan as recorded in the Changuan cejin and began to contemplate it himself. There are three main reasons for this vision. First, one cannot find in the Hakuin Annals anything about the person who gave Hakuin the mu kōan. Second, there is no evidence of Hakuin having contemplated the mu kōan before encountering the Changuan cejin. Third, we can see records of the combination of the Changuan cejin and the contemplation of the mu character kōan. ‘During the entire trip, Hakuin was deeply absorbed in the samadhi of (Changuan) cejin. He contemplated the mu kōan’ (行程、深く策進三昧に入る. 狗子佛性の話に參ず. ……一卓一擧、長途、無の字を失せずして行く) (N51, 505) and ‘With (Changuan) cejin as his instructor, he contemplated every day and night’(策進を以て善知識と爲して、日夜研究すること累日) (N62, 510). The Changuan cejin is widely read in China as a textbook that teaches how to contemplate the mu character kōan, and many people who have read this book have begun the kōan exercise on their own and have become enlightened. See Noguchi, ‘Kanna Zen ni okeru Zenkan sakushin no ichizuke’, 218.98. H3.172: 岩頭老人猶お好在なり.99. H3.180–84.100. H3.194–97; 8.154–56.101. H3.195.102. H9.436.103. Although the three parts of seeing one’s nature, seeking bodhi above, and cultivating sentient beings below are indispensable in Hakuin’s system of practice, he also described correct practice from another angle as follows: ‘If one has only “seeing one’s own nature” but not the dharma, one will not be able to move forward, like a chariot lacking one of the two wheels. If one only has dharma but cannot “see one’s nature”, one is like a parrot that speaks without knowing’(見性抛教片輪轂,教缺見性解語鸚) (K1.274). The dharma is to be collected and applied for the sake of cultivating sentient beings below, and the ability to discern the meaning of dharma and levels of beings is to be cultivated by seeking bodhi above.104. See the section 1.2.2. ‘The Superiority of Zen’ in this article.105. H7.139–40: 一見して、感涙肝に銘じ、信根骨に徹して、踏舞を忘る.106. H12.43: 大憤志を發して、晝夜に精彩を著け、單 々 に無の字を擧揚 シ.107. H9.426–27: 片時 モ 休 マズ. ……晝夜眠 ラズ、寢食共 ニ 忘 ル。忽然 トシテ 大疑現前 シテ、……只 ダ 無 ノ 字有 ルノミ. ……此 ノ 如 キ 者數日、乍 チ 一夜、鐘聲 ヲ 聽 イテ 發轉.108. H3.180; K2.1131.109. H7.170.110. H9.429–30.111. H7.173–74: 轉 々 悟らば轉 々 參ぜよ、轉 々 了せば轉 々 擧せよ. 身を終る迄休罷する事なかれ.112. K1.606.113. According to the Yaemugura, fascicle 3, Shōju bestowed Hakuin two kinds of practices as ‘the practice after insight’: (1) ‘keeping continuous mindfulness without slacking off for a moment’(正念工夫、相續不斷) and ‘the wheel of the four great vows’ (四弘の誓願輪) (H7.179–80). The former means to cut off delusions by contemplating kōans and corresponds to seeking bodhi above. For the latter, see Yoshizawa, Hakuin: Zenga no sekai, 263–266; idem, Hakuin zenji no fushigi na sekai, 40-41; idem, ‘Hakuin zenga wo yomu’, 13–16.114. H9.331115. K1.572116. K1.703–07, 717–22.117. H14.237; O6.361: 悟りても下化行衆生の心なきは、魔道に墮つと春日野の敕.118. H8.154-156.119. H3.195-96: 馬年既に八旬餘に到れども、終に怠墮せず、請に應じ五十里百里を經ると雖も、少しも恐れず分に隨いて法施を行ず.120. Nishimura, Tōrei oshō nenpu, 102; O1.286–87.121. Yanagi, ‘Hakuin Ekaku to Bodaishin no han’.122. H6.247: 西天の四七, 東土の二三,的 々 相承し, 心傳祕授の一大事義, 初發心時より便成正覺の曉に到る迄, 少も怠惰すべからざる底の正修なり.123. Regarding Dahui Zonggao’s Kanna Zen exercise, please refer to Zhang, ‘Songdai Kanhua chan xingcheng shi zongzhu’.124. Changuan cejin (1600 edition) was compiled by Yunqi Zhuhong 雲棲袾宏 (1535–1615), one of the three eminent monks of the Wanli 萬曆 period (1563–1620). According to his tomb inscription, the text was written to clarify that ‘the joint practice of Chan and Pure land are both from the one mind’ (禪淨雙修, 不出一心). See Yanagi, Eimei Enju to Sugyōroku no kenkyū, 343. The Changuan cejin was first published in Japan in 1656 and was republished in 1762 by Hakuin’s dharma heir, Tōrei. According to the commentary, Hakuin treated the chanting of the Buddha in the text as something that ‘should be eliminated altogether’ (一齊削去可) and required to remove all passages in the text about chanting the name of Amitābha Buddha, and to read it exclusively as a manual of kōan exercise. See Fujiyoshi, ‘Zenkan Sakushin ni okeru Zen to Nenbutsu no Mondai’. Furthermore, Yunqi’s position on ‘joint cultivation of Chan and Pure land’ (禪淨雙修) is at odds with Hakuin’s focus on only one specific practical experience. Hakuin criticised Yunqi’s method as a ‘darkness in the eye that see’s one’s nature, and is weak in reaching the profound truth’ (見性眼暗 ク、參玄力 ラ 乏 シ) (H2.121; H9.496, O2.402).125. H3.233–34, 316; H4.150; H7.116: 大悟十八度、小悟數を知らず.126. Noguchi, ‘Daie Sōkō to Taigo Shōgo no niku’.127. H3.316; H4.150: 大歡喜を得る者大凡六七回、其の餘の小悟、怡悦、蹈舞を忘るる者數を知らず.128. O3.244: 爾來、四十二に到る. 其の中間に大歡喜を得る者、大凡十餘度.129. The several experiences mentioned earlier—the realization of the mysteries of the five stages, grasping the ‘method of correct mindfulness, continuous without interruption’ (正念工夫、相續不斷), the understanding of the true meanings of the Xuedou’s gāthā (Jp. Geju 偈頌), the Avataṃsaka Sūtra and the Vimalakīrti Sūtra—for Hakuin these were affirmed through experiencing insights. Hakuin described the joy gained from the mysteries of the five stages, understanding the mysteries of the five stages, and the true doctrine of the Avataṃsaka Sūtra as ‘unbearable happiness’ (K1.606, 703). He described the understanding of the Vimalakīrti Sūtra as ‘limitless happiness’ (K1.717). These descriptions are the same as those used by Hakuin when describing the joy of great insights. The number of great insights described by Hakuin mentioned in this article is stated as ‘attaining great joy six or seven times’ (大歡喜を得る者大凡六七回) and ‘the times I attained great joy numbered over ten’ (大歡喜を得る者、大凡十餘度) (H3.316, H4.150; O3.244).130. Yanagi, ‘Hakuin Ekaku to Bodaishin no Han’.131. O1.367. Almost the same content can be seen in an article on his twenty-ninth year in the Ryūtaku sōken Tōrei Ji rō oshō nenpu 龍澤創建東嶺慈老和尚年譜 (see pages 137 and O 1.296-297). Here I quoted the more concise of the two. In addition, there are two types of Tōrei’s chronology: a personally written draft by his disciple Daikan Monju 大觀文殊 (1766–1842) and a publication in the eleventh year of Kansē (1799). The former has a commentary on Nishimura, which is the Tōrei Oshō Nenpu, while the text of the latter is included in the Hakuin oshō zenshū (O1.267–368). In addition, the combined electronic versions of the texts for the written draft of Daikan, Nishimura’s chronology, and the Hakuin Oshō Zenshū have been published on the homepage of the Hanazono Daigaku Kokusai Zengaku Kenkyūjo (http://iriz.hanazono.ac.jp/frame/data_f00d5_011.html).Additional informationFundingThis article has received the research subsidy of the JSPS [JP17H00904, 20K00060, 21K00060].