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 z_4, if z_4 cooks, then z_4 is a sailor. Richard is playing tennis if and only if Sarah is a sailor. Richard is not playing tennis. Sarah is cooking or Sarah is not a sailor.
If Sarah were a sailor, then Sarah is cooking can be inferred via the rewriting rule. If Richard plays tennis, then Sarah is a sailor can be inferred via the biconditional elimination rule. If Sarah were a sailor, then Richard is playing tennis can be inferred via the biconditional elimination rule. Sarah is not a sailor can be inferred via the biconditional elimination rule.