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 Barbara were poor, then John is not writing a letter. John is writing a letter. Jessica is drinking water. Barbara is poor if and only if Michael is playing tennis.
Barbara is not poor can be inferred via the modus tollens rule. John is writing a letter and Jessica is drinking water can be inferred via the conjunction rule. Jessica is drinking water and John is writing a letter can be inferred via the conjunction rule. If Barbara were poor, then Michael is playing tennis can be inferred via the biconditional elimination rule. If Michael plays tennis, then Barbara is poor can be inferred via the biconditional elimination rule.