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: forall x_15: R_15(x_15) -> S_15(x_15). r -> R_15(a_15). q <-> r.
q -> r can be inferred via the biconditional elimination rule. r -> q can be inferred via the biconditional elimination rule.