\chapter{Sequence numbers}
\label{chp:sequence-numbers}
These quantities are not available directly, but are held to determine how out-of-date the user's record of jobs or variables
may be.

Every time you read a job or variable record, the sequence number of the job or variable list is checked, and if out-of-date, you will receive
the error \filename{\constprefix{}SEQUENCE}. This is not so much of an error as a warning. If you re-read the job or variable required,
then you will not receive this error, except where you and one or more other users have ``raced'' to update a
variable and you have ``lost the race''.

If you want to bypass this, you can access the job or variable without worrying about the sequence using the \textit{flag
}\filename{\constprefix{}IGNORESEQ}, however you might receive an error about unknown job or variable if the job or variable has
disappeared. In the case of variables you may still receive the \filename{\constprefix{}SEQUENCE} error if another user
``wins a race'' as described above.

