What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: It is sunny or Mary is not happy. It is overcast if and only if Mary is happy.
If Mary were happy, then it is sunny can be inferred via the rewriting rule. If it is overcast, then Mary is happy can be inferred via the biconditional elimination rule. If Mary were happy, then it is overcast can be inferred via the biconditional elimination rule.