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 a janitor if and only if it is sunny. If Thomas were a janitor, then it is sunny. It is not sunny.
Thomas is not a janitor can be inferred via the modus tollens rule. If Thomas were a janitor, then it is sunny can be inferred via the biconditional elimination rule. If it is sunny, then Thomas is a janitor can be inferred via the biconditional elimination rule. Thomas is not a janitor can be inferred via the biconditional elimination rule.