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: William is not a police officer. William is a police officer if and only if William is playing squash. For all x_22, x_22 is a sailor or x_22 will sleep. For all x_22, x_22 is not a sailor.
If William were a police officer, then William is playing squash can be inferred via the biconditional elimination rule. If William plays squash, then William is a police officer can be inferred via the biconditional elimination rule. William is not playing squash can be inferred via the biconditional elimination rule. For all x_22, x_22 will sleep can be inferred via the universal disjunctive syllogism rule.