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: Robert is not a sailor. If Thomas takes a plane, then Sarah is working. For all z, if z cooks, then z is a sailor. If Sarah works, then Robert is cooking. If Sarah works, then Thomas is taking a plane.
If Thomas takes a plane, then Robert is cooking can be inferred via the transitivity rule. Thomas is taking a plane if and only if Sarah is working can be inferred via the biconditional introduction rule. Sarah is working if and only if Thomas is taking a plane can be inferred via the biconditional introduction rule.