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_18, x_18 is a lawyer. For all x_18, x_18 is a lawyer if and only if x_18 will write a letter. For all x_18, if x_18 works, then x_18 is writing a letter.
For all x_18, if x_18 were a lawyer, then x_18 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_18, if x_18 writes a letter, then x_18 is a lawyer can be inferred via the universal biconditional elimination rule.