  This is an expanded version of the author's talk at the third annual meeting
of International Consortium of Chinese Mathematicians held at USTC in December
2020. In this expository article, we give a survey on joint works with Hosono,
Lian, and Yau in arXiv:2003.07148 and arXiv:2008.04039. We also carry out some
explicit examples to illustrate our results in enumerative geometry which will
appear in our forthcoming papers.
