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 Charles listens to a song, then Barbara is sleeping. If Charles listens to a song, then Barbara is sleeping. If Barbara sleeps, then Charles is listening to a song.
Charles is listening to a song if and only if Barbara is sleeping can be inferred via the biconditional introduction rule. Charles is listening to a song if and only if Barbara is sleeping can be inferred via the biconditional introduction rule. Barbara is sleeping if and only if Charles is listening to a song can be inferred via the biconditional introduction rule. Barbara is sleeping if and only if Charles is listening to a song can be inferred via the biconditional introduction rule.