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: Charles is a soldier if and only if Robert is an electrician. Sarah is not sleeping. If Charles were a soldier, then Sarah is sleeping. If Charles were a soldier, then it is sunny. If it is sunny, then Robert is an electrician.
Charles is not a soldier can be inferred via the modus tollens rule. If Charles were a soldier, then Robert is an electrician can be inferred via the transitivity rule. If Charles were a soldier, then Robert is an electrician can be inferred via the biconditional elimination rule. If Robert were an electrician, then Charles is a soldier can be inferred via the biconditional elimination rule.