EXSYS is a program for running expert system knowledge bases.  Expert
systems are programs that allow the computer to emulate a human expert in
a subject area.  The computer will ask you questions and arrive at a
conclusion.  The program can explain why it needs the information it is
requesting and can explain its conclusions.

The program will ask you a series of questions by displaying a statement
with a numbered list of alternatives that could finish the statement.
Enter the number or numbers of the items in the list correct for your
situation. If more than one number is desired, separate the numbers with a
comma or space. If you wish to know why the question is being asked,
enter "WHY" and the computer will display the rule it is using.

The computer may also need numeric or text data.  The program will tell you
what information it needs and ask you to input the value.  Again, if you
input "WHY" the computer will show you the rule it is testing.

Rules are expressed in the IF-THEN-ELSE format.  If ALL of the statements
in the IF part are true, the rule is true and the THEN statements are 
considered to be true and added to what the program knows.  If any of
the statements in the IF part are false, the rule is  false, and any 
statements in the ELSE part are then taken to be true and added to what
the program knows.

The statements in the rule are English sentences or algebraic expressions
and should be easily readable.

The THEN and ELSE parts may also contain the possible solutions that EXSYS
will select among.  These solutions are indicated by a statement followed
by " - Probability = " and are followed by a ratio that indicates the
likelihood of the solution. The closer the ratio is to 1 the more likely
the solution is.

The computer will attempt to derive information from other rules rather
than ask the user.  This is called backward chaining.  If you ask "WHY"
the computer needs information, more than one rule may be displayed.
This is because the first rule is being used to derive information needed
by the second etc., down to the final rule which is the actual rule being
tested.

If you would like more details on the meaning of the question being asked,
press <?> in answer to the question.  The author of the knowledge base
may have created a file of information on the various questions.  If 
such a file has been created, additional information will be displayed.
If there is no such file, the program will tell you.

When a rule is displayed, you may ask the computer how it knows the
rule's IF conditions are true by entering the line number of the IF
statement.  The computer will either tell you that you told the program
the statement was true or display the rule that was used to derive the
information.  If a rule is in the process of being tested, the program
may respond that it does not know if the statement you have questioned is
true.  If you ask about a mathematical expression, the program will show
the value of each of the variables.  You may then ask how the program
arrived at each of these values. The reference for a rule can be
requested by pressing the <R> key.

When the computer has arrived at its conclusions it will display an ordered
list of the possible solutions with their final scores.  The program may
also display additional notes or calculated values that were determined
by the program.  You may ask how it arrived at any of these results by
entering the line number in question and the appropriate rules that were
used will be displayed. You may print the list if you wish.

A very useful feature once you have arrived at the list of solutions, is
to change one or more of the answers you input to see how it changes the
results.  To do this press the <C> key and you will have a list of all
the input you provided displayed.  Enter the number of the item you wish
to change.  When all of the changes are made, press <R> to re-run the data.
The program may ask you additional questions if your changes necessitate
additional information in reaching conclusions.  The program will display
the new sorted list of choices with both the previous and new values
for comparison. (You have the option to switch off the display of the
previous values.)

When you are finished, press <D> and you will have the option of running
the program again.

You also have the option of saving the data you have entered into the
computer and being able to return to the place you left off later.
If you wish to quit the program, enter QUIT in response to any of the
requests for information.  The program will then ask for the name of
the file you want to store the data in.  DO NOT USE THE NAME OF THE
KNOWLEDGE BASE or you could accidentally erase part of the knowledge
base.  When you run the program, one of the first things you will be
asked is if you want to restore data from a file. If you press [Y], the
program will ask you for the name of the file to read the data from, and
will return you to the point that you QUIT previously.