=External Links=
* [http://www.top-5000.nl/authors/rebel/chess840.htm#PAWN-EXT Extension Techniques in REBEL (pawn)] from [http://www.top-5000.nl/authors/rebel/chess840.htm Programmer Corner ] by [[Ed Schroder|Ed Schröder]] <ref>How Rebel Plays Chess is also available as [http://members.home.nl/matador/Inside%20Rebel.pdf pdf reprint]</ref>
* [http://www.frayn.net/beowulf/theory.html#extend Computer Chess Programming Theory - Search Extensions] by [[Colin Frayn]]
