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 Elisabeth plays tennis, then Charles is a taxi driver. Charles is not a taxi driver. If Elisabeth writes a letter, then Elisabeth is playing tennis.
Elisabeth is not playing tennis can be inferred via the modus tollens rule. If Elisabeth writes a letter, then Charles is a taxi driver can be inferred via the transitivity rule.