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 it is late, then Thomas is making tea. If Thomas makes tea, then Elisabeth is not sad. Elisabeth is sad. If Thomas makes tea, then it is late.
Thomas is not making tea can be inferred via the modus tollens rule. If it is late, then Elisabeth is not sad can be inferred via the transitivity rule. It is late if and only if Thomas is making tea can be inferred via the biconditional introduction rule. Thomas is making tea if and only if it is late can be inferred via the biconditional introduction rule.