如何形式化地表示索引

集合{ri}表示索引集合,i从0到n。
chrome-extension://ikhdkkncnoglghljlkmcimlnlhkeamad/pdf-viewer/web/viewer.html?file=https%3A%2F%2Faclanthology.org%2F2022.acl-long.340.pdf

集合{ri}表示索引集合,i从0到n。
chrome-extension://ikhdkkncnoglghljlkmcimlnlhkeamad/pdf-viewer/web/viewer.html?file=https%3A%2F%2Faclanthology.org%2F2022.acl-long.340.pdf