Finding

Exists

System.Collections.Generic.List<int> mylist; 
mylist = new System.Collections.Generic.List<int>(); 
mylist.Add(10); 
mylist.Add(20); 
if (mylist.Exists(x => x == 20) == false) 
{ 
} 

First

If you try and use First when there are no values, an exception will be thrown

FirstOrDefault

If you try and use FirstOrDefault when there are no values, the default value will be returned instead of an exception

How to quickly find a particular item anything equivalent to a Dictionary - ContainsKey ?