Consider the following premises. David is a lawyer if and only if Susan is a sailor. For all x_12, x_12 will drive a car if and only if x_12 is a janitor. For all x_12, x_12 will not drive a car. For all x_12, x_12 is a janitor if and only if x_12 is a lawyer. Can we infer the following from them? Susan is a sailor.
 From the fact that for all x_12, x_12 will drive a car if and only if x_12 is a janitor, and that for all x_12, x_12 will not drive a car we can infer that for all x_12, x_12 is not a janitor. From the fact that for all x_12, x_12 is a janitor if and only if x_12 is a lawyer, and that for all x_12, x_12 is not a janitor we can infer that for all x_12, x_12 is not a lawyer. From the fact that for all x_12, x_12 is not a lawyer we can infer that David is not a lawyer. Finally, from the fact that David is a lawyer if and only if Susan is a sailor, and that David is not a lawyer we can infer that Susan is not a sailor, which contradicts that Susan is a sailor. Therefore, the answer is no.