@book{PPN591917149, title = {Die Buchstabenrechnung Theil 1}, series = {GDML\_Books}, publisher = {Duncker u. Humblot}, address = {Berlin}, year = {1833}, language = {de}, url = {http://dml.mathdoc.fr/item/PPN591917149} }
Egen, Peter Nikolaus Caspar. Die Buchstabenrechnung Theil 1. GDML_Books (1833), http://gdmltest.u-ga.fr/item/PPN591917149/