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 y_4, y_4 will go running if and only if y_4 is a police officer. For all y_4, y_4 is a sailor if and only if y_4 is a police officer. There is at least one y_4 for which y_4 is not a sailor.
For all y_4, if y_4 goes running, then y_4 is a police officer can be inferred via the universal biconditional elimination rule. For all y_4, if y_4 were a sailor, then y_4 is a police officer can be inferred via the universal biconditional elimination rule. For all y_4, if y_4 were a police officer, then y_4 is running can be inferred via the universal biconditional elimination rule. For all y_4, if y_4 were a police officer, then y_4 is a sailor can be inferred via the universal biconditional elimination rule. There is at least one y_4 for which y_4 is not a police officer can be inferred via the existential biconditional elimination rule.