There exists three system tables, named SYSTEM.CATALOG, SYSTEM.STATS, SYSTEM.SEQUENCE respectively, in Phoenix4.2.1, but no find any documents to introduce these tables' purpose.   if dropped anyone once, what side-effect will it produce? and how to recover it?
BTW, it looks like that the SEQUENCE function is no effect after dropped the SYSTEM.SEQUENCE, if my applications surely don't use  SEQUENCE function forever, whether or not i can drop the table?