T. de Melo e Silva Johnson. Federal University of Pernambuco, Recife, Brazil, (2005)ndltd.org (oai:agregador.ibict.br.BDTD_UFPE:oai:repositorio.ufpe.br:123456789/2083).
T. Johnson. Federal University of Minas Gerais, Belo Horizonte, Brazil, (2009)ndltd.org (oai:agregador.ibict.br.BDTD_UFMG:oai:bibliotecadigital.ufmg.br:MTD2BR-FAFI-82TFQJ).
J. Johnson. Secondary School Mathematics in the World of Communication Technology, volume 119 of IFIP Conference Proceedings, page 68-70. Chapman & Hall, (1997)