title: C#. How to assign a bool variable certain value (not true and not false)?
body: <p>How to assign to a bool variable certain value (not true and not false)?
  I guess it can be so-called <strong>null</strong> state.
  But I'm not sure if it's correct guess. And I have no clue how to do that.
  Moreover, how to do that with possible further assignation (true/false)?</p>