Consider the following premises. For all x_1, if x_1 plays tennis, then x_1 is a sailor. For all x_1, if x_1 reads a book, then x_1 is climbing a mountain. There is at least one x_1 for which if x_1 were a sailor, then x_1 is reading a book. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_1 for which if x_1 plays tennis, then x_1 is climbing a mountain.
 From the fact that there is at least one x_1 for which if x_1 were a sailor, then x_1 is reading a book, and that for all x_1, if x_1 reads a book, then x_1 is climbing a mountain we can infer that there is at least one x_1 for which if x_1 were a sailor, then x_1 is climbing a mountain via existential transitivity. Finally, from the fact that for all x_1, if x_1 plays tennis, then x_1 is a sailor, and that there is at least one x_1 for which if x_1 were a sailor, then x_1 is climbing a mountain we can infer that there is at least one x_1 for which if x_1 plays tennis, then x_1 is climbing a mountain via existential transitivity. Therefore, the answer is yes.