Consider the following premises. For all x_6, x_6 is fast. For all x_6, if x_6 were a mechanic, then x_6 is not fast. For all x_6, x_6 is curious if and only if x_6 is a mechanic. There is at least one x_6 for which x_6 is a doctor if and only if x_6 is curious. Can we infer the following from them? There is at least one x_6 for which x_6 is not a doctor.
 From the fact that for all x_6, if x_6 were a mechanic, then x_6 is not fast, and that for all x_6, x_6 is fast we can infer that for all x_6, x_6 is not a mechanic. From the fact that for all x_6, x_6 is curious if and only if x_6 is a mechanic, and that for all x_6, x_6 is not a mechanic we can infer that for all x_6, x_6 is not curious. Finally, from the fact that there is at least one x_6 for which x_6 is a doctor if and only if x_6 is curious, and that for all x_6, x_6 is not curious we can infer that there is at least one x_6 for which x_6 is not a doctor. Therefore, the answer is yes.