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: Mary is a server or Elisabeth is not a nurse. If Mary were a server, then Elisabeth is a nurse. If Elisabeth were a nurse, then Mary is a server.
If Elisabeth were a nurse, then Mary is a server can be inferred via the rewriting rule. Mary is a server if and only if Elisabeth is a nurse can be inferred via the biconditional introduction rule. Elisabeth is a nurse if and only if Mary is a server can be inferred via the biconditional introduction rule.