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_2, if y_2 were a sailor, then y_2 is an electrician. For all y_2, y_2 is not a sailor. There is at least one y_2 for which if y_2 were an electrician, then y_2 is a sailor.
There is at least one y_2 for which y_2 is not an electrician can be inferred via the existential modus tollens rule. There is at least one y_2 for which y_2 is an electrician if and only if y_2 is a sailor can be inferred via the existential biconditional introduction rule. There is at least one y_2 for which y_2 is a sailor if and only if y_2 is an electrician can be inferred via the existential biconditional introduction rule.