Consider the following premises. There is at least one x_4 for which if x_4 plays squash, then x_4 is running. For all x_4, x_4 will take a plane if and only if x_4 will go running. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_4 for which if x_4 plays squash, then x_4 is taking a plane.
 From the fact that for all x_4, x_4 will take a plane if and only if x_4 will go running we can infer that for all x_4, if x_4 goes running, then x_4 is taking a plane via universal biconditional elimination. Finally, from the fact that there is at least one x_4 for which if x_4 plays squash, then x_4 is running, and that for all x_4, if x_4 goes running, then x_4 is taking a plane we can infer that there is at least one x_4 for which if x_4 plays squash, then x_4 is taking a plane via existential transitivity. Therefore, the answer is yes.