@online{
   timsrc,
   author = "Kokkotas, Kostas D.",
   title = "Lecture Introduction to General Relativity, 12. Lesson",
   publisher = "Universität Tübingen",
   year = "2009",
   month = "Jan",
   day = "21",
   url = "https://timms.uni-tuebingen.de:443/tp/UT_20090121_001_relativ_0001",
   urldate = "2024-04-24"
}