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: t -> u_4. ~r. u_4 <-> r. p <-> t.
u_4 -> r can be inferred via the biconditional elimination rule. p -> t can be inferred via the biconditional elimination rule. r -> u_4 can be inferred via the biconditional elimination rule. t -> p can be inferred via the biconditional elimination rule. ~u_4 can be inferred via the biconditional elimination rule.