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, if y makes tea, then y is a cashier. There is at least one y for which y will write a letter if and only if y is a cashier. For all y, if y writes a letter, then y is making tea.
For all y, if y writes a letter, then y is a cashier can be inferred via the universal transitivity rule. There is at least one y for which if y writes a letter, then y is a cashier can be inferred via the existential biconditional elimination rule. There is at least one y for which if y were a cashier, then y is writing a letter can be inferred via the existential biconditional elimination rule.