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 listening to a song if and only if Charles is a poet. If Charles sleeps, then Charles is a poet. Robert is playing squash or David is not listening to a song.
If David listens to a song, then Robert is playing squash can be inferred via the rewriting rule. If David listens to a song, then Charles is a poet can be inferred via the biconditional elimination rule. If Charles were a poet, then David is listening to a song can be inferred via the biconditional elimination rule.