@online{ timsrc, author = "Kokkotas, Kostas D.", title = "Lecture Introduction to General Relativity, 8. Lesson", publisher = "Universität Tübingen", year = "2008", month = "Dec", day = "10", url = "https://timms.uni-tuebingen.de:443/tp/UT_20081210_001_relativ_0001", urldate = "2024-03-29" }