@online{ timsrc, author = "Kokkotas, Kostas D.", title = "Lecture Introduction to General Relativity, 1. Lesson", publisher = "Universität Tübingen", year = "2008", month = "Oct", day = "15", url = "https://timms.uni-tuebingen.de:443/tp/UT_20081015_001_relativ_0001", urldate = "2024-11-11" }