Advanced QL
===========

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Topics on advanced uses of QL. These topics assume that you are familiar with the QL language and the basics of query writing.

-  :doc:`Semantics of abstract classes <abstract-classes>`
-  :doc:`Choosing appropriate ways to constrain types <constraining-types>`
-  :doc:`Determining the most specific types of a variable <determining-specific-types-variables>`
-  :doc:`Folding predicates <folding-predicates>`
-  :doc:`Understanding the difference between != and not(=) <equivalence>`
-  :doc:`Monotonic aggregates in QL <monotonic-aggregates>`
