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 z, if z were a writer, then z is reading a book. For all z, if z reads a book, then z is a writer. There is at least one z for which if z were a writer, then z is reading a book.
For all z, z is a writer if and only if z will read a book can be inferred via the universal biconditional introduction rule. For all z, z will read a book if and only if z is a writer can be inferred via the universal biconditional introduction rule. There is at least one z for which z is a writer if and only if z will read a book can be inferred via the existential biconditional introduction rule. There is at least one z for which z will read a book if and only if z is a writer can be inferred via the existential biconditional introduction rule.