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_2, if x_2 were a lawyer, then x_2 is writing a letter. For all x_2, x_2 is an office clerk if and only if x_2 will write a letter. For all x_2, if x_2 were an office clerk, then x_2 is a lawyer.
For all x_2, if x_2 were an office clerk, then x_2 is writing a letter can be inferred via the universal transitivity rule. For all x_2, if x_2 were an office clerk, then x_2 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_2, if x_2 writes a letter, then x_2 is an office clerk can be inferred via the universal biconditional elimination rule.