I am following the OpenFTA (Fault Tree Analysis) User Manual at http://www.openfta.com/Download.aspx. Page 81 uses the inclusion/exlusion expansion to express the top-most fault in terms of minimal cut sets. Page 82 shows the same inclusion/expansion expansion broken up into components. However, it looks like there are typographical errors. 1) I suspect that the P1's are suppose to be P1, P2, P3, etc. based on the implied definition of Pi just before mid-page. 2) The third component [P3, if my point (1) above is correct] should have an addition rather than a subtraction. 3) The paragraph following the P1/P2/P3 says that each line has N-choose-r sub-terms. This should be N-choose-i (and N should not be capital). 4) In the same sentence, it says there are 2N terms. I believe this should be 2^N (same as the normal inclusion/exlusion expansion). I am new to FTA and I arrived at the above 4 point by surfing the web for information on FTA. Can anyone confirm this? Thanks.