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 x_12, x_12 is not a server. For all x_12, if x_12 were a poet, then x_12 is not making tea. For all x_12, x_12 will write a letter or x_12 will make tea. For all x_12, x_12 is a doctor if and only if x_12 is a server. For all x_12, if x_12 writes a letter, then x_12 is a doctor.
For all x_12, if x_12 were a doctor, then x_12 is a server can be inferred via the universal biconditional elimination rule. For all x_12, if x_12 were a server, then x_12 is a doctor can be inferred via the universal biconditional elimination rule. For all x_12, x_12 is not a doctor can be inferred via the universal biconditional elimination rule.