During a campus survey you asked a large number of students about their favorite film directors, and then you input the data into a relational database. The schema

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R$($NetID$,$ FavDirector$)$ does not support lists of strings, that is$,$ if a student has multiple favorite directors, that information will take multiple rows in the relation. Now a friend of yours wants you to find out who has either Sergio Leone $($SL$)$ or Quentin Tarantino $($QT$)$ as their favorite film directors, but not both. How would you formulate this query using a relational algebra expression?