Consider the following premises. t -> u. W_1(a_10) or t. forall y: S(y) <-> W_1(y). S(a_10) -> u. Can we infer u from them? If possible, name the inference rules being used at each step.
 From forall y: S(y) <-> W_1(y) we can infer forall y: W_1(y) -> S(y) via universal biconditional elimination. From forall y: W_1(y) -> S(y) we can infer W_1(a_10) -> S(a_10) via universal instantiation. From W_1(a_10) -> S(a_10), S(a_10) -> u we can infer W_1(a_10) -> u via transitivity. Finally, from W_1(a_10) -> u, t -> u, W_1(a_10) or t we can infer u via disjunction elimination. Therefore, the answer is yes.