What's the relationship between Yuan Tiangang and Li?

Yuan Tiangang is Li's master. Yuan Tiangang (now Chengdu, Sichuan) was born in Chengdu, Yizhou, a metaphysician and astronomer in the late Sui and early Tang Dynasties, and a native of Yongxian, Li. He was an astronomer, mathematician and calendar calculator in the Tang Dynasty. Yuan Tiangang was Li's teacher. They were all men of insight in the late Sui Dynasty and had lofty ideals. Yuan Tiangang once built a house in front of Panlong Mountain in Langzhou. Li admired his name for a long time, so he came from afar with gold bars and knocked at the door.