Two nested NOT EXISTS can be used to express a SELECT statement that embodies the notion of “for all (logical ∀) the values in a column, there exists (logical ∃) …”
For example the query to select a ‘true’ value if the library has at least one book for all the publishers can be expressed as follows:
SELECT 'TRUE' WHERE NOT EXISTS (SELECT * FROM publisher pb WHERE NOT EXISTS (SELECT * FROM book bk WHERE pb.PubNum=bk.PubNum);