produce a single expression using the standard set and relation operators, such that the expression can be interpreted as answering the query correctly, for any data set. Your answers should use only the set and relation symbols given above in addition to terms standing for constant elements of or , plus the following operators:

• set union
• set intersection
• set difference
• relational range () for some set , or () for some specific element .
• relational inverse 1
• relational composition which generalizes composition of functions

  ():=,()().

  In other words, is related to in if starting at you can follow an arrow to the start of an arrow and then follow the arrow to get to .
• The set of endorsers who have recommended pages containing the word discrete
• The relation that relates endorser and word iff has recommended a page containing
• The set of pages that have at least one incoming or outgoing link
• The relation that relates word and page iff appears on a page that links to