In the remaining parts you may use the fact that the resolution proof system is "sound". That is if a set of clauses is satisfied by some truth assignment a derived clause also must be satisfied by that truth assignment. Assume we had a rule that from 4 clauses {x,y}, {-x,y} and {-x,y} would allows us to directly derive the empty clause. Explain why it would be wrong (undesirable) to have this rule. In the remaining parts you may use the fact that the resolution proof system is "sound". That is if a set of clauses is satisfied by some truth assignment a derived clause also must be satisfied by that truth assignment. Assume we had a rule that from 4 clauses {x,y}, {-x,y} and {-x,y} would allows us to directly derive the empty clause. Explain why it would be wrong (undesirable) to have this rule