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 mechanic, then y_2 is working. For all y_2, if y_2 were a server, then y_2 is a mechanic. There is at least one y_2 for which if y_2 works, then y_2 is a mechanic.
For all y_2, if y_2 were a server, then y_2 is working can be inferred via the universal transitivity rule. There is at least one y_2 for which y_2 will work if and only if y_2 is a mechanic can be inferred via the existential biconditional introduction rule. There is at least one y_2 for which y_2 is a mechanic if and only if y_2 will work can be inferred via the existential biconditional introduction rule.