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 Richard plays tennis, then it is cloudy. If it is cloudy, then Richard is playing tennis. If it is late, then Richard is playing tennis.
If it is late, then it is cloudy can be inferred via the transitivity rule. Richard is playing tennis if and only if it is cloudy can be inferred via the biconditional introduction rule. It is cloudy if and only if Richard is playing tennis can be inferred via the biconditional introduction rule.