James C. Owen of KSBC has kindly provided PDF'ized versions of Dr Charles Forgy's thesis, where he defines the RETE algorithm (Charles Forgy is the inventor of the RETE algorithm, which is kind of important to rule engines ;).
For those who are interest in this, you can find them here. They are broken down by chapter as they are pretty large. There is a whole lotta history here (which I thoroughly enjoy). The 70's and 80's were a golden age for software (and music !).