Pressing <R> will display the reference for the rule if there is one.  This
will provide the basis for the rule.

If you wish to know why the computer considers one of the IF conditions to be
true, enter the line number of the IF condition.  The computer will respond
with information on the origin of the information:

     1. The computer may display another rule which was used to derive the IF
    condition.  This new rule will have the qualifier you are asking about in
    its THEN or ELSE part.  You may then ask how the computer knows that
    rule's IF conditions are true.

    2. If the information came from asking you for input, the computer will
    tell you that you told it the condition was true.

    3. If the condition you are asking about has not been checked yet, the
    computer will tell you it does not yet know if it is true.

    4. Occasionally the computer may have just derived new information and
    will tell you the condition is false and the rule will be ignored.

    5. If the statement was a mathematical expression, the program will
    display the value of each of the variables in the expression. If you want
    to know how the value for a particular variable was determined,enter the
    line number of the variable.  The program will then explain how that
    value was arrived at.

    6. If the information came from an external program that was called,
    the program will tell you what program returned the data.

The computer will re-display the rule after each question. Press just <ENTER>
when you are through asking about the rule.
