Most published math papers are answers to open questions posed by the authors of the papers, right? So why is this problem that the paper responds to is never explicit in the text by the authors? Would not that be an important thing since it would save time for other mathematicians not to waste time formulating problems that have already been answered? Or is an expert in the field able to identify the open problem that a particular paper responds to even if it is not explicit in the text? Could someone explain to me in detail how this works?