Consider the following premises. For all x_10, x_10 is an office clerk or x_10 is not a sailor. For all x_10, if x_10 were an office clerk, then x_10 is a sailor. Thomas is an office clerk. Can we infer the following from them? If we can, name the inference rule being used: For all x_10, x_10 is not a sailor.
 From the fact that Thomas is an office clerk we can infer that there is at least one x_10 for which x_10 is an office clerk via existential generalization. From the fact that for all x_10, x_10 is an office clerk or x_10 is not a sailor we can infer that for all x_10, if x_10 were a sailor, then x_10 is an office clerk via universal rewriting. From the fact that for all x_10, if x_10 were an office clerk, then x_10 is a sailor, and that for all x_10, if x_10 were a sailor, then x_10 is an office clerk we can infer that for all x_10, x_10 is an office clerk if and only if x_10 is a sailor via universal biconditional introduction. From the fact that for all x_10, x_10 is an office clerk if and only if x_10 is a sailor we can infer that for all x_10, if x_10 were an office clerk, then x_10 is a sailor via universal biconditional elimination. Finally, from the fact that for all x_10, if x_10 were an office clerk, then x_10 is a sailor, and that there is at least one x_10 for which x_10 is an office clerk we can infer that there is at least one x_10 for which x_10 is a sailor via existential modus ponens, which contradicts that For all x_10, x_10 is not a sailor. Therefore, the answer is no.