# Develop Solution Manual for Textbook Questions

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}

(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 $S \subset (S \cup T)$.