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: For all x_12, if x_12 cooks, then x_12 is a doctor. Jessica is not a doctor. For all x_12, if x_12 were a doctor, then x_12 is cooking. If Jessica doesn't cook, then Thomas is taking a plane.
For all x_12, x_12 will cook if and only if x_12 is a doctor can be inferred via the universal biconditional introduction rule. For all x_12, x_12 is a doctor if and only if x_12 will cook can be inferred via the universal biconditional introduction rule.