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_1. p -> s. t_1 -> s. s -> t_1.
~s can be inferred via the modus tollens rule. p -> t_1 can be inferred via the transitivity rule. t_1 <-> s can be inferred via the biconditional introduction rule. s <-> t_1 can be inferred via the biconditional introduction rule.