Middle School Mathematics Allied Publishers (2008) Arithmetic and Beginning Science S. Bertram FastPencil Inc (2010) The Cosmic Sphere K.K. Sewell Nova Publishers (199)
Robert Kaplan, Oxford University Press (book, 1999) Origin of the numerals, Zero concept Ahmed Boucenna, ePrint arXiv:0707.3579 (article, 2007) Much ado about nothing: An introductive inquiry about zero Lionello Pogliani et. al., International Journal of Mathematical Education in Science and Technology (article, 2006) How was zero discovered? Nils-Bertil Wallin, YaleGlobal (article, 2002) Babylonian Pythagoras’ theorem, the early history of zero and a polemic on the study of the history of science Rahul Roy, Resonance (article, 2003)