Consider the following premises. For all x_6, x_6 will not make tea. There is at least one x_6 for which if x_6 works, then x_6 is an artist. For all x_6, if x_6 were an artist, then x_6 is working. For all x_6, x_6 will work if and only if x_6 will make tea. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_6 for which x_6 is not an artist.
 From the fact that for all x_6, x_6 will work if and only if x_6 will make tea, and that for all x_6, x_6 will not make tea we can infer that for all x_6, x_6 will not work via universal biconditional elimination. From the fact that there is at least one x_6 for which if x_6 works, then x_6 is an artist, and that for all x_6, if x_6 were an artist, then x_6 is working we can infer that there is at least one x_6 for which x_6 will work if and only if x_6 is an artist via existential biconditional introduction. Finally, from the fact that there is at least one x_6 for which x_6 will work if and only if x_6 is an artist, and that for all x_6, x_6 will not work we can infer that there is at least one x_6 for which x_6 is not an artist via existential biconditional elimination. Therefore, the answer is yes.