 
 <prompt> Wetin no be di main solution? Based on di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: The second way wey dem take solve the problem na based on the idea of class, and e define set as class wey dey belong to other classes, while proper class na class wey no dey belong to other classes. Under the Zermelo-Fraenkel approach, the axioms dey prevent the construction of a set wey get all sets wey no dey belong to themselves. But under the von Neumann approach, the class of all sets wey no dey belong to themselves fit be constructed, but e go be proper class and no be set. 