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