@online{
   timsrc,
   author = "Kokkotas, Kostas D.",
   title = "Lecture Introduction to General Relativity, 4. Lesson",
   publisher = "Universität Tübingen",
   year = "2008",
   month = "Nov",
   day = "05",
   url = "https://timms.uni-tuebingen.de:443/tp/UT_20081105_001_relativ_0001",
   urldate = "2024-04-20"
}