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: Elisabeth is a writer. Sarah is not running. Sarah is running if and only if Thomas is writing a letter. If Sarah goes running, then Thomas is writing a letter.
Elisabeth is a writer and Sarah is not running can be inferred via the conjunction rule. Sarah is not running and Elisabeth is a writer can be inferred via the conjunction rule. If Sarah goes running, then Thomas is writing a letter can be inferred via the biconditional elimination rule. If Thomas writes a letter, then Sarah is running can be inferred via the biconditional elimination rule. Thomas is not writing a letter can be inferred via the biconditional elimination rule.