@article{ELMA_1980__35_141250,
     author = {Wulf Rehder},
     title = {On the commutativity of two projections.},
     journal = {Elemente der Mathematik},
     pages = {120--122},
     publisher = {mathdoc},
     volume = {35},
     year = {1980},
     zbl = {0415.47002},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1980__35_141250/}
}