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 drinks water, then Robert is listening to a song. If Robert listens to a song, then Richard is drinking water. Richard is drinking water.
Robert is listening to a song can be inferred via the modus ponens rule. Richard is drinking water if and only if Robert is listening to a song can be inferred via the biconditional introduction rule. Robert is listening to a song if and only if Richard is drinking water can be inferred via the biconditional introduction rule.