/// <summary>
/// This returns the result set of: (A\B) U (B\A) U (A Intersection B)
///
/// Example:
///
/// A = { A, B }
/// B = { A, C }
///
/// A\B = { B } || The elements that are in A but not in B
/// B\A = { C } || The elements that are in B but not in A
/// A Intersection B = { A } || The elements that are in both A and B
///
/// result = { B, C, A }! All unique variables from two different sets.
/// </summary>
/// <returns>A list representing the set of all unique variables in the proposition formula.</returns>
public override List <Proposition> GetVariables()
{
List <Proposition> leftChildVariables = LeftSuccessor.GetVariables();
List <Proposition> rightChildVariables = RightSuccessor.GetVariables();
return(leftChildVariables.Except(rightChildVariables). // Set difference gets applied { A } \ { B }
Union(rightChildVariables.Except(leftChildVariables)). // { B } \ { A }
Union(leftChildVariables.Intersect(rightChildVariables)).ToList()); // { A } Intersection { B }, resulting in a set containing all unique elements (unordered though)
}
