Keyword is a sequence of alphabetic characters and possibly some special characters. All keywords fall into two categories: reserved keywords, which cannot be used as symbolic names, and non-reserved keywords, which being recognized by context can be used as symbolic names.
Reserved keywords are the following:
and else mod union by if not within cross in or diff inter symdiff div less then
Non-reserved keywords are described in following sections.
All the keywords have fixed meaning, which will be explained on discussion of corresponding syntactic constructions, where the keywords are used.