Leo Geurts; Lambert Meertens; Steven Pemberton. <a href="http://www.cwi.nl/~steven/abc"><cite>The ABC Programmer's Handbook.</cite></a> Prentice-Hall. ISBN: 0-13-000027-2. URL: <a href="http://www.cwi.nl/~steven/abc">http://www.cwi.nl/~steven/abc</a>