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: p <-> u. forall x: Q_1(x) -> U(x). p -> q_6. q_6 -> Q_1(d).
p -> Q_1(d) can be inferred via the transitivity rule. p -> u can be inferred via the biconditional elimination rule. u -> p can be inferred via the biconditional elimination rule.