1. http://www.cs.nott.ac.uk/~gmh/faq.html. http://www.cs.nott.ac.uk/~gmh/faq.html.
2. Brodie Leo Starting Forth 2nd ed. 1987 Prentice-Hall Englewood Cliffs NJ pg. 119 Brodie Leo Starting Forth 2nd ed. 1987 Prentice-Hall Englewood Cliffs NJ pg. 119
3. http://amazon.com. http://amazon.com.
4. http://www.latrobe.edu.au/philosophy/phimvt/ http://www.latrobe.edu.au/philosophy/phimvt/