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_11 -> q. p_11 <-> u. q -> p_11.
p_11 <-> q can be inferred via the biconditional introduction rule. q <-> p_11 can be inferred via the biconditional introduction rule. p_11 -> u can be inferred via the biconditional elimination rule. u -> p_11 can be inferred via the biconditional elimination rule.