I have a struct and a list as follow, I just wanted to sort the Inputpoints according to date. I have used the following commands but I can not see any sorting.  public struct Points {     public Date Date;     public double Quantity; } _test = new List&lt;Points&gt;(InputPoints); _test.OrderBy(t =&gt; t.Date);
I'm using C# on Framework 3.5.  I'm looking to quickly sort a Generic List&lt;T&gt;.  For the sake of this example, let's say I have a List of a Person type with a property of lastname.  How would I sort this List using a lambda expression?  List&lt;Person&gt; people = PopulateList(); people.OrderBy(???? =&gt; ?????)
I am trying to show that: \begin{equation} \frac{n}{\phi(n)} = \sum_{d \mid n} \frac{\mu^2(d)}{\phi(d)} \end{equation} where $\phi(n)$ is  and $\mu$ is the .  The identity clearly holds for $n=1$, so if we write $n=p_1^{a_1} \cdots p_k^{a_k}$ for the prime decomposition of $n$, the left-hand side becomes: \begin{eqnarray*} \frac{n}{\phi(n)} &amp; = &amp; \frac{p_1^{a_1} \cdots p_k^{a_k}}{\phi(p_1^{a_1}) \cdots \phi(p_k^{a_k})} \\ &amp; = &amp; \frac{p_1^{a_1} \cdots p_k^{a_k}}{(p_1^{a_1-1})(p_1-1) \cdots (p_k^{a_k})(p_k-1)} \\ &amp; = &amp; \frac{p_1 \cdots p_k}{(p_1-1)\cdots (p_k-1)} \end{eqnarray*}   Whereas the right-hand side becomes:  \begin{eqnarray*} \sum_{d \mid n} \frac{\mu^2(d)}{\phi(d)} &amp; = &amp; \sum_{\substack{d \mid n \\ p^2 \nmid d}} \frac{1}{\phi(d)} \\ &amp; = &amp; 1 + \frac{1}{\phi(p_1)} + \dots + \frac{1}{\phi(p_k)} + \frac{1}{\phi(p_1 p_2)} + \dots + \frac{1}{\phi(p_{k-1}p_k)} \\ &amp; + &amp; \dots + \frac{1}{\phi(p_1 \cdots p_k)} \\ &amp; = &amp; 1 + \frac{1}{p_1 - 1} + \dots + \frac{1}{p_k - 1} + \frac{1}{(p_1 - 1)(p_2 - 1)} + \dots + \frac{1}{(p_{k-1}-1)(p_k-1)} \\ &amp; + &amp; \dots + \frac{1}{(p_1 - 1) \cdots (p_k - 1)} \end{eqnarray*}  I am unsure of how to proceed from this point however. 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