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_20: R_20(x_20) -> S_20(x_20). R_20(a_20) <-> q. S_20(a_20) <-> r.
R_20(a_20) -> q can be inferred via the biconditional elimination rule. S_20(a_20) -> r can be inferred via the biconditional elimination rule. q -> R_20(a_20) can be inferred via the biconditional elimination rule. r -> S_20(a_20) can be inferred via the biconditional elimination rule.