{{sfn | Born | Ehlers | Pössel | 2003 | p=}}

* {{cite book | last=Born | first=Max | last2=Ehlers | first2=Jürgen | last3=Pössel | first3=Markus | title=Die Relativitätstheorie Einsteins | publisher=Springer | publication-place=Berlin Heidelberg | date=2003 | isbn=3-540-00470-X | language=de}}

<ref name="i030">{{cite book | last=Born | first=Max | last2=Ehlers | first2=Jürgen | last3=Pössel | first3=Markus | title=Die Relativitätstheorie Einsteins | publisher=Springer | publication-place=Berlin Heidelberg | date=2003 | isbn=3-540-00470-X | language=de | page=}}</ref>