@article{AMLG_1972__15_137874,
     author = {Horst Osswald},
     title = {Unterstruktur-Invariante {Formeln} in der intuitionistischen {Logik.}},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {118--128},
     publisher = {mathdoc},
     volume = {15},
     year = {1972},
     zbl = {0263.02014},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1972__15_137874/}
}