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: Thomas is sad or Mary is an office clerk. If David were a lawyer, then Mary is a cashier. Thomas is not sad or David is a lawyer. Mary is a cashier if and only if Mary is an office clerk.
Mary is an office clerk or David is a lawyer can be inferred via the resolution rule. If Mary were a cashier, then Mary is an office clerk can be inferred via the biconditional elimination rule. If Mary were an office clerk, then Mary is a cashier can be inferred via the biconditional elimination rule.