Stan demonstrates a third independent verification (besides QueryCalc
and MPEX) that December 31, 9999 is indeed a Friday:

>From HP-UX & AIX:
>
>   cal 12 9999
>          December 9999
>   Sun Mon Tue Wed Thu Fri Sat
>                1   2   3   4
>    5   6   7   8   9  10  11
>   12  13  14  15  16  17  18
>   19  20  21  22  23  24  25
>   26  27  28  29  30  31
>

I very much appreciate the verification. When I programmed up the
calendar & calendar functions (i.e., number of days between two points
in time, etc.) in QueryCalc several years ago, I did it purely on
theoretical grounds. While the program itself is relatively simple, I've
gotten to the point that I don't trust anything that isn't independently
verified several different ways. Small errors often show up only when a
program is pushed to its limits.

Speaking of limits, Stan also writes that the UNIX command CAL also
works for any year between the year 1 and 10000:

>   AIX:     cal 1 10000
>   0702-001 Specify month as number between 1 and 12
>           Specify year as number between 1 and 9999.
>

In that, UNIX blows the doors off of QueryCalc. I limited QC's calendar
to only the years 1583 to 9999. 1583 was the first complete year of the
modern Gregorian calendar. As the author of a report writer, I didn't
feel that going back any further was necessary -- as no one was likely
to have any invoices outstanding any farther back than that, or much
chance of collecting if they did.

My question is: what does UNIX do about the missing days in October,
1582? And if UNIX really does handle October correctly, why would it
want to philosophically limit itself to only the Year 1? The Julian
Calendar (365 days in a year, every fourth year a leap year) that Pope
Gregory replaced (every fourth year a leap year, except those divisible
by 100, except when divisible by 400) was first implemented in 46 B.C.
Does UNIX not only skip the missing days but also automatically change
its algorithm from the Gregorian counting scheme to the Julian method
prior to October, 1582? If it doesn't, the days of the weeks reported
prior to that date will be wrong. These are important questions -- and
inquiring minds want to know.

As an aside, actually neither Gregory nor Julius of course devised the
calendars that were named after them. They were written out by
astronomers. In Julius Caesar's instance, the astronomer whose calendar
Julius Caesar adopted was Sosigenes' of Egypt. In honor of Julius
Caesar's doing that, the Roman Senate passed a special resolution
renaming the "fifth" month, Quintilis, (which had become the seventh
month by that time), "July", in his honor. When Augustus Caesar came to
power, he demanded an equal-time resolution (literally), thus the
"sixth" month, Sextilis, was renamed "August". If the tradition had
continued, September, the "seventh" month would now be known as "Tiber",
but the Roman Senate told Tiberius enough was enough.

Wirt Atmar