I just worked through an exercise of Jehle and Reny (2011), Advanced Microeconomic Theory and was wondering if we shall, as a community, develop solution manuals for textbooks which are frequently used. Let me provide an example. It is askaed to show that (p. 546)

A1.2 The following are intuitively 'obvious'. Give a proof for each one \begin{align} &(a) ~ S \subset (S \cup T).\\ &(b) ~ T \subset (S \cup T).\\ &(c) ~ (S \cap T) \subset S.\\ &(d) ~ (S \cap T) \subset T. \end{align}

My suggested answer.

(a) Suppose $x \in S$ and $x \in T$. Since $(S \cup T) := \{x : x \in S \text{ or } x \in T\}$ we must have $x \in S \Rightarrow x \in (S \cup T)$ which is the condition for $S \subset (S \cup T)$.

First off all I'm not sure if the answer is correct, since I'm not a mathematician by training and never took real analysis. However, I'd be glad if the community would confirm the result. If the answer I provided was not true, we could work out the true solution. We could collect verified answers in some proper .pdf document and provide it.

Disclaimer: No idea about legal issues. I reckon publishers wanna make money with solution manuals, too?!

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  • $\begingroup$ What exactly are you asking? If anyone would join in the task, if anyone knows the legal side or if you should start posting individual questions and answers on the site? $\endgroup$ – Giskard Dec 9 '15 at 9:27
  • $\begingroup$ I was thinking about organizing solved textbook exercises in a systematic way. Take this wikibooks for instance where they already figured a roadmap, but which still contains blank entries en.wikibooks.org/wiki/Introduction_to_Game_Theory. Is it possible to create that kind of structured register within the stack exchange site? $\endgroup$ – clueless Dec 10 '15 at 13:11
  • $\begingroup$ Making a solutions manual and tagging all the questions with the book would basically be the mother-load of doing a bunch of homework questions for people. It would just be time consuming. More useful would be for us to start making a collection of important econ theorems and their proofs (e.g. Kakutani fixed point to prove existence of competitive prices) $\endgroup$ – Kitsune Cavalry Dec 19 '15 at 0:54

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