Consider the following premises. For all x_13, if x_13 makes tea, then x_13 is taking a plane. For all x_13, x_13 will take a plane if and only if x_13 will make tea. For all x_13, x_13 will take a plane if and only if x_13 is a mechanic. For all x_13, x_13 is not a mechanic. Can we infer the following from them? There is at least one x_13 for which x_13 will make tea.
 From the fact that for all x_13, x_13 will take a plane if and only if x_13 is a mechanic, and that for all x_13, x_13 is not a mechanic we can infer that for all x_13, x_13 will not take a plane. From the fact that for all x_13, x_13 will take a plane if and only if x_13 will make tea we can infer that for all x_13, if x_13 takes a plane, then x_13 is making tea. From the fact that for all x_13, if x_13 makes tea, then x_13 is taking a plane, and that for all x_13, if x_13 takes a plane, then x_13 is making tea we can infer that for all x_13, x_13 will make tea if and only if x_13 will take a plane. From the fact that for all x_13, x_13 will make tea if and only if x_13 will take a plane we can infer that for all x_13, if x_13 makes tea, then x_13 is taking a plane. Finally, from the fact that for all x_13, if x_13 makes tea, then x_13 is taking a plane, and that for all x_13, x_13 will not take a plane we can infer that for all x_13, x_13 will not make tea, which contradicts that There is at least one x_13 for which x_13 will make tea. Therefore, the answer is no.