Consider the following premises. There is at least one x_11 for which x_11 is poor. For all x_11, x_11 is a sailor if and only if x_11 is an electrician. For all x_11, x_11 will drink water or x_11 is a sailor. For all x_11, if x_11 were an electrician, then x_11 is writing a letter. For all x_11, if x_11 drinks water, then x_11 is an electrician. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_11 for which x_11 is poor and x_11 will write a letter.
 From the fact that for all x_11, x_11 is a sailor if and only if x_11 is an electrician we can infer that for all x_11, if x_11 were a sailor, then x_11 is an electrician via universal biconditional elimination. From the fact that for all x_11, if x_11 drinks water, then x_11 is an electrician, that for all x_11, if x_11 were a sailor, then x_11 is an electrician, and that for all x_11, x_11 will drink water or x_11 is a sailor we can infer that for all x_11, x_11 is an electrician via universal disjunction elimination. From the fact that for all x_11, if x_11 were an electrician, then x_11 is writing a letter, and that for all x_11, x_11 is an electrician we can infer that for all x_11, x_11 will write a letter via universal modus ponens. Finally, from the fact that there is at least one x_11 for which x_11 is poor, and that for all x_11, x_11 will write a letter we can infer that there is at least one x_11 for which x_11 is poor and x_11 will write a letter via existential conjunction. Therefore, the answer is yes.