I boxed myself to a corner with this design.  I wanted classes
implementing X to necessarily implement IEquatable.  I thought I'd go
the C++ CRTP route and came up with this.

interface X<T> : IEquatable<T>
{
}

class XImpl : X<XImpl>
{
}

class XImpl_2 : X<XImpl_2>
{
}

then I had a class to manage a collection of objects implementing X

class X_Collection<T> where T : X<T>
{
  private LinkedList<T> XCollection = new LinkedList<T>();
}

Now I am stuck here.

How do I declare an instance of X_Collection when I have no idea what
T would be at that point?  The only thing I can do is:

class someClass
{
  private X_Collection<XImpl> col = new X_Collection<XImpl>();
}

I don't want that since the whole idea is to use the X_Collection
class to keep track of *any* object that implements X<T>.

I seem to be in some kind of recursive nightmare.

Can anyone help?