Hi, Have checked the boolean expression in vol 4. link: http://www.allaboutcircuits.com/vol_4/chpt_8/8.html The examples has the output of Out = (A+B+C+/D)(A+B+/C+D)(A+/B+C+/D)(A+/B+/C+D)(/A+/B+/C+D)(/A+B+C+/D)(/A+B+/C+D) but i think it should be like this. Out = (A+B+C+/D)(/A+B+/C+D)(A+/B+C+/D)(A+/B+/C+D)(/A+/B+/C+D)(/A+B+C+/D)(/A+B+/C+D) The 2nd expression should have A bar on the top. note: I used "/" as Bar on the top of the letter. If the expression is wrong then the computation should be changed. Thanks.