Арапски бројеви — разлика између измена

* {{Cite book|ref=harv |last=Lumpkin| first = Beatrice| last2=Strong| first2 = Dorothy| title = Multicultural science and math connections: middle school projects and activities| publisher = Walch Publishing|year=1995|url=https://books.google.com/?id=2LgG8lsJQmAC&pg=PA118|isbn=978-0-8251-2659-8|pages=118}}

* {{Cite book|ref=harv |last=Schipp| first = Bernhard| last2=Krämer| first2 = Walter| title = Statistical Inference, Econometric Analysis and Matrix Algebra: Festschrift in Honour of Götz Trenkler| publisher = [[Springer Science+Business Media|Springer]]|year=2008|url=https://books.google.com/?id=t6XfLJzqO_kC&pg=PA387|isbn=978-3-7908-2120-8|pages=387}}

* {{Cite book|ref=harv |last=Thorndike| first = Edward| title = The Thorndike Arithmetics, Book One| publisher = BiblioBazaar, LLC|year=2008|url=https://books.google.com/?id=y3agVFn5HMoC&pg=PA102|isbn=978-0-559-24262-5|pages=102}}