Consider the following premises. For all x_17, x_17 will sleep if and only if x_17 is an electrician. For all x_17, if x_17 were poor, then x_17 is working. For all x_17, if x_17 climbs a mountain, then x_17 is working. For all x_17, if x_17 works, then x_17 is an electrician. There is at least one x_17 for which x_17 will climb a mountain. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_17 for which x_17 is an electrician.
 From the fact that there is at least one x_17 for which x_17 will climb a mountain we can infer that there is at least one x_17 for which x_17 will climb a mountain or x_17 is poor via existential addition. From the fact that for all x_17, if x_17 climbs a mountain, then x_17 is working, that for all x_17, if x_17 were poor, then x_17 is working, and that there is at least one x_17 for which x_17 will climb a mountain or x_17 is poor we can infer that there is at least one x_17 for which x_17 will work via existential disjunction elimination. From the fact that for all x_17, x_17 will sleep if and only if x_17 is an electrician we can infer that for all x_17, if x_17 sleeps, then x_17 is an electrician via universal biconditional elimination. From the fact that there is at least one x_17 for which x_17 will work we can infer that there is at least one x_17 for which x_17 will work or x_17 will sleep via existential addition. Finally, from the fact that for all x_17, if x_17 works, then x_17 is an electrician, that for all x_17, if x_17 sleeps, then x_17 is an electrician, and that there is at least one x_17 for which x_17 will work or x_17 will sleep we can infer that there is at least one x_17 for which x_17 is an electrician via existential disjunction elimination. Therefore, the answer is yes.