Let R be a relation schema and R be a relation with respect to R. Let S be a relation schema and S be a relation with respect to S. We assume that LaTeX: R\cap S e\varnothing R S . Show formally (without examples) that the outer-join operator R S is a derived Relational Algebra operator. That is, it can be expressed by the 5 (+1) basic Relational Algebra operators. You are allowed to make use of derived Relational Algebra operators that have already been shown to be derived in class. Explain your definition afterwards