Consider the following premises. For all x_7, x_7 is a sailor if and only if x_7 is a police officer. For all x_7, if x_7 reads a book, then x_7 is a sailor. For all x_7, if x_7 plays tennis, then x_7 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_7 for which the fact that x_7 plays tennis does not imply that x_7 is a police officer.
 From the fact that for all x_7, x_7 is a sailor if and only if x_7 is a police officer we can infer that for all x_7, if x_7 were a sailor, then x_7 is a police officer via universal biconditional elimination. From the fact that for all x_7, if x_7 plays tennis, then x_7 is reading a book, and that for all x_7, if x_7 reads a book, then x_7 is a sailor we can infer that for all x_7, if x_7 plays tennis, then x_7 is a sailor via universal transitivity. Finally, from the fact that for all x_7, if x_7 plays tennis, then x_7 is a sailor, and that for all x_7, if x_7 were a sailor, then x_7 is a police officer we can infer that for all x_7, if x_7 plays tennis, then x_7 is a police officer via universal transitivity, which contradicts that There is at least one x_7 for which the fact that x_7 plays tennis does not imply that x_7 is a police officer. Therefore, the answer is no.