@online{
   timsrc,
   author = "Kokkotas, Kostas D.",
   title = "Lecture Introduction to General Relativity, 9. Lesson",
   publisher = "Universität Tübingen",
   year = "2008",
   month = "Dec",
   day = "17",
   url = "https://timms.uni-tuebingen.de:443/tp/UT_20081217_001_relativ_0001",
   urldate = "2024-04-19"
}