title: Find unique value in group of groups
body: <p>Guess i have two groups</p>
  
  <pre><code>using System.Collections.Generic;
  
  namespace ConsoleApplication
  {
      internal class Student
      {
          public string Name;
          public string Surname;
          public int Mark;
      }
  
      internal class Program
      {
          private static void Main()
          {
              var twoGroups = new List&lt;List&lt;Student&gt;&gt;
              {
                  new List&lt;Student&gt;
                  {
                      new Student { Name = "Anna",  Surname = "Mors",  Mark = 4 }, 
                      new Student { Name = "Jimmy", Surname = "Lemon", Mark = 4 }
                  },
                  new List&lt;Student&gt;
                  {
                      new Student { Name = "Anna",  Surname = "Mors",   Mark = 4 }, 
                      new Student { Name = "Tommy", Surname = "Wojski", Mark = 4 },
                      new Student { Name = "Jimmy", Surname = "Lemon",  Mark = 4 }
                  }
              };
          }
      }
  }
  </code></pre>
  
  <p>How can i get unique persons from both groups (by Name or any other property) with linq?</p>
  
  <p>It's obvious there is Tommy, but i dont know how can i pick him with linq (or pick a list of unique persons.</p>
  
  <p><strong><em>UPD</em></strong></p>
  
  <p>Also, can i pick group contain only unique student.</p>
  
  <pre><code>using System.Collections.Generic;
  
  namespace ConsoleApplication
  {
      internal class GroupOfStudents
      {
          public string Code;
          public List&lt;Student&gt; Students;
      }
  
      internal class Student
      {
          public string Name;
          public string Surname;
          public int Mark;
      }
  
      internal class Program
      {
          private static void Main()
          {
              var twoGroups = new List&lt;GroupOfStudents&gt;
              {
                  new GroupOfStudents
                  {
                      Code = "A1",
                      Students = new List&lt;Student&gt;
                      {
                          new Student { Name = "Anna",  Surname = "Mors",  Mark = 4 }, 
                          new Student { Name = "Jimmy", Surname = "Lemon", Mark = 4 }
                      }
                  },
                  new GroupOfStudents()
                  {
                      Code = "B2",
                      Students = new List&lt;Student&gt;
                      {
                          new Student { Name = "Anna",  Surname = "Mors",   Mark = 4 }, 
                          new Student { Name = "Tommy", Surname = "Wojski", Mark = 4 },
                          new Student { Name = "Jimmy", Surname = "Lemon",  Mark = 4 }
                      }
                  }
              };
          }
      }
  }
  </code></pre>
  
  <p>I think i need to pick student and push him to new Group with same name, right?</p>