Question 1116635
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4.  H           2,1,3 Resolution <br>
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The rule of Resolution in propositional logic says that if  AvB (AvB is true if either A or B is true) and  (~AvC) (A is not true or C is true) then one can immediately resolve this to  BvC (BvC is true if either B or C is true).   This is so because A and ~A appear in two disjunctions involving B and C, respectively.    To see why this is, assume A is true.  Then the disjunction ~A v C is only true if C is true.   If A is not true, then the disjunction A v B is true only if B is true, thus we can conclude, independent of A,  BvC (BvC is true if B or C is true).   <br>

In the posted problem, 1 says "not M  and S"  while 2 affirms "not M."   Since 3 says "M or H or not S" we can look at 3 and say, we know  "not M" (so "H or not S" must be true) but 1 refutes "not S" so that leaves H as true.