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: If Mary were happy, then Robert is drinking water. It is raining. Mary is not happy. If Robert drinks water, then Mary is happy.
Robert is not drinking water can be inferred via the modus tollens rule. It is raining and Mary is not happy can be inferred via the conjunction rule. Mary is not happy and it is raining can be inferred via the conjunction rule. Mary is happy if and only if Robert is drinking water can be inferred via the biconditional introduction rule. Robert is drinking water if and only if Mary is happy can be inferred via the biconditional introduction rule.