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_8, x_8 is a scientist. For all x_8, if x_8 were fast, then x_8 is not a scientist. For all x_8, x_8 is fast if and only if x_8 will write a letter.
For all x_8, x_8 is not fast can be inferred via the universal modus tollens rule. For all x_8, if x_8 were fast, then x_8 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 writes a letter, then x_8 is fast can be inferred via the universal biconditional elimination rule.