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). S_20(a_20) <-> w. R_20(a_20) <-> t.
S_20(a_20) -> w can be inferred via the biconditional elimination rule. R_20(a_20) -> t can be inferred via the biconditional elimination rule. w -> S_20(a_20) can be inferred via the biconditional elimination rule. t -> R_20(a_20) can be inferred via the biconditional elimination rule.