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: David is sleeping if and only if it is overcast. Charles is not fast. If Mary plays a game, then Charles is fast. If it is cold, then Mary is playing a game. If it is overcast, then it is cold.
Mary is not playing a game can be inferred via the modus tollens rule. If it is cold, then Charles is fast can be inferred via the transitivity rule. If it is overcast, then Mary is playing a game can be inferred via the transitivity rule. If David sleeps, then it is overcast can be inferred via the biconditional elimination rule. If it is overcast, then David is sleeping can be inferred via the biconditional elimination rule.