This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
The intersection of two sets A and B is defined as the set that contains all the elements of A that also appear in B, but no other elements.
When the object returned by this method is enumerated, Intersect<TSource> enumerates first, collecting all distinct elements of that sequence. It then enumerates second, marking those elements that occur in both sequences. Finally, the marked elements are yielded in the order in which they were collected.
The default equality comparer, Default, is used to compare values of the types that implement the IEqualityComparer<T> generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.