COMMENT ON 'AN ALGORITHM FOR EXACT FAULT-TREE PROBABILITIES WITHOUT CUT SETS' BY L. B. PAGE, ET AL.

A direct evaluation algorithm was presented by L. B. Page and J. E. Perry (1986) that is based on a bottom-up modularization of the faul tree and a top-down recursive probability calculation. The point is made here that direct evaluation techniques that do not use cut sets have not been taken seriously in the past and that one reason for this is that recursion is not permitted in Fortran, which is the language used by most engineers. Several additional computer codes that evaluate a fault tree directly are described. One of the codes is written in PL/1, and uses techniques of pattern-recognition and list-processing to evaluate fault-tree probabilities. Two other codes illustrate the use of Lisp and Prolog to implement recursive algorithms for the direct evaluation of fault trees.