Consider the following premises. S_21(a_21) -> R_21(a_21). S_21(a_21) <-> r_1. r_2 -> R_21(a_21). ~r_1. forall x_21: R_21(x_21) -> S_21(x_21). Can we infer r_2 -> R_21(a_21) from them?
That is one of the premises. Therefore, the answer is yes.