- Problem 6 ( 7 marks). Recall that a language D can describe a set X, if there is an onto function E:DX. This implies that XD and tells us that every element of X has at least one D-description. In each case below, indicate whether Xi is describable by Di. If your answer is no, explain why; if your answer is yes, then for each xX, give a possible D-description of x. X1={nnN,n