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: John is running if and only if it is windy. If it is windy, then Susan is writing a letter. Susan is not writing a letter.
It is not windy can be inferred via the modus tollens rule. If John goes running, then it is windy can be inferred via the biconditional elimination rule. If it is windy, then John is running can be inferred via the biconditional elimination rule.