4. Decide whether the following argument is valid. If it is valid argument, give a formal proof (i.e., justify which laws of logic need to be applied to each of the premises, in a sequence of arguments, to arrive at the conclusion). If the argument is invalid (i.e., you cannot find a sequence of laws that leads from the premises to the conclusion), show that it is invalid by finding an appropriate assignment of truth values to the propositional variables. Premises: p (q r), s r, r p. Prove: s q.