rameters are
    read from the standard input device as a part of the
    initialisation process.  The result returned by the program is
    written to the standard output device as a part of the
    finalisation process.

<pre>
PROGRAM GCD (x : INTEGER; y : INTEGER) : INTEGER;

BEGIN
    WHILE x # y DO
        IF x > y
            THEN x := x - y
            ELSE y := y - x
        END
    END;
    RETURN x
END GCD.
</pre>

    The factorial program below uses a constant declaration to define
    the limit