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: If John were a writer, then Barbara is playing squash. Sarah is not a poet. John is a writer if and only if James is a carpenter. If Barbara plays squash, then Sarah is a poet.
Barbara is not playing squash can be inferred via the modus tollens rule. If John were a writer, then James is a carpenter can be inferred via the biconditional elimination rule. If James were a carpenter, then John is a writer can be inferred via the biconditional elimination rule.