These are the three basic sitautions in which parties are deemed necessary to be joined to a lawsuit. Could you please give examples of each of these/explain each more in basic/easy to understand terms? Thanks.

19(a)(1)(A): the person's absence would preclude the court from providing complete relief

2.Or the person has an interest in the action that could be impaired if the person is absent

3.Or the person's absence could result in multiple or inconsistent obligations on an existing party