Shortened footnote and citation:
{{sfn | Lehmann | Schulz | 2007 | p=}}
* {{cite book | last=Lehmann | first=Ingmar | last2=Schulz | first2=Wolfgang | title=Mengen - Relationen - Funktionen | publisher=Vieweg+Teubner Verlag | publication-place=Wiesbaden | date=2007-03-15 | isbn=978-3-8351-0162-3 | language=de}}
Named reference:
<ref name="y639">{{cite book | last=Lehmann | first=Ingmar | last2=Schulz | first2=Wolfgang | title=Mengen - Relationen - Funktionen | publisher=Vieweg+Teubner Verlag | publication-place=Wiesbaden | date=2007-03-15 | isbn=978-3-8351-0162-3 | language=de | page=}}</ref>