Consider the following premises. p_3 <-> S_12(a_12). forall x_12: R_12(x_12) <-> S_12(x_12). p_3 or R_12(a_12). Can we infer S_12(a_12) from them?
 From forall x_12: R_12(x_12) <-> S_12(x_12) we can infer R_12(a_12) <-> S_12(a_12). From R_12(a_12) <-> S_12(a_12) we can infer R_12(a_12) -> S_12(a_12). From p_3 <-> S_12(a_12) we can infer p_3 -> S_12(a_12). Finally, from p_3 -> S_12(a_12), R_12(a_12) -> S_12(a_12), p_3 or R_12(a_12) we can infer S_12(a_12). Therefore, the answer is yes.