Le 29/03/2013 15:08, Stavros Macrakis a ?crit : > In your example, 'r' is not an explicit rational number (e.g. 5 or 2/3 > or -15/7) but a symbol. Thank you very much for this explanation. Regards -- Jean-Fran?ois MAUREL PIMECA http://www.pimeca.com