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: Robert is not a carpenter. If Barbara plays squash, then Robert is a carpenter. If Thomas sleeps, then Elisabeth is not sad. Elisabeth is sad.
Barbara is not playing squash can be inferred via the modus tollens rule. Thomas is not sleeping can be inferred via the modus tollens rule. Robert is not a carpenter and Elisabeth is sad can be inferred via the conjunction rule. Elisabeth is sad and Robert is not a carpenter can be inferred via the conjunction rule.