@article{AMLG_1981__21_137979,
     author = {Hugo Volger},
     title = {A unifying approach to theorems on preservation and interpolation for binary relations between structures.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {101--112},
     publisher = {mathdoc},
     volume = {21},
     year = {1981},
     zbl = {0482.03012},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1981__21_137979/}
}