Consider the following premises. forall y: R_3(y) <-> R_4(y). R_4(i) -> R_3(i). Can we infer R_3(i) <-> R_4(i) from them? If possible, name the inference rules being used at each step.
We can infer R_3(i) <-> R_4(i) via the universal instantiation rule. Therefore, the answer is yes.