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, x will write a letter if and only if x is a janitor. For all x, x will write a letter or x is a carpenter. For all x, x is not a janitor. For all x, x will play tennis.
For all x, if x writes a letter, then x is a janitor can be inferred via the universal biconditional elimination rule. For all x, if x were a janitor, then x is writing a letter can be inferred via the universal biconditional elimination rule. For all x, x will not write a letter can be inferred via the universal biconditional elimination rule.