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_10, x_10 will not write a letter. For all x_10, x_10 is a lawyer or x_10 is a janitor. There is at least one x_10 for which x_10 will cook. For all x_10, x_10 is a lawyer if and only if x_10 will write a letter.
For all x_10, if x_10 were a lawyer, then x_10 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_10, if x_10 writes a letter, then x_10 is a lawyer can be inferred via the universal biconditional elimination rule. For all x_10, x_10 is not a lawyer can be inferred via the universal biconditional elimination rule.