My last note had an error in it, and the code originally sent to the list should be ignored. I have attached the current version of the code, and here is some further information (the behavior is different, by the way, but still apparently wrong). I have attached the current version of the program, which behaves slightly differently from the version originally sent. I am running ghc 6.6, gcc 4.1.2, g++ 4.1.1, on Debian Linux. The compile lines are ghc -threaded solve.hs or ghc -threaded -O2 solve.hs. The execution line is ./a.out, which should give me single-threaded execution. Ignore the output on stdout; it is the same for both versions. On stderr, the unoptimized version of the attached code gives me both "fail" and "goOn" (see lines #150 and #153). The optimized version gives me only "goOn." I think that both should give me both "fail" and "goOn." Were circumstances different, I might suspect that laziness and optimization had something to do with this. However, earlier tests showed inconsistency between the result of the test in gTst3 and the code where the value of gTst3 is used. A copy of the current version of solve.hs is attached. Best, Murray Gross P.S.: For anyone who has actually looked at the logic, I am aware that the test in gTst3 can be sharpened. That will come later. The current version is adequate for the time being.