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: ~u. t and r_1. u or ~u_4.
~u_4 can be inferred via the disjunctive syllogism rule. t can be inferred via the simplification rule. r_1 can be inferred via the simplification rule. u_4 -> u can be inferred via the rewriting rule.