cols ← {base←1} ##.mayan numb               ⍝ Mayan numbers.

As  the Pre-Columbian people of Central America used their toes as well as their
fingers for counting, they wound up with a base 20 (vigesimal) number system.

In earlier writings, distinct symbols were used to represent different powers of
20:
       1 - dot
      20 - hatchet or flag
     400 - feather
    8000 - purse or incense pouch

For  example,  if  ⍟,  ⍞, ↑, $ represent pictograms of dot, hatchet, feather and
purse respectively, then

    $ $ ↑ ⍞ ⍞ ⍞ ⍟ ⍟ ⍟ ⍟  →  20⊥2 1 3 4 →  16464

An APL function to decode such strings might be:

      deco←{20⊥+/'$↑⍞⍟'∘.=⍵~' '}

      deco'$ $ ↑ ⍞ ⍞ ⍞ ⍟ ⍟ ⍟ ⍟'
16464

By  the 10th century AD, this had evolved into a positional system in which dig-
its  1-19 were expressed as dots '⍟' arranged in 4 rows (hands/feet) of 5 (fing-
ers/toes).  For  legibility,  completed  rows  of  5  were drawn as a solid line
'⌹⌹⌹⌹⌹'  and  multi-digit  numbers were written in columns with more significant
digit-blocks (higher powers of 20) uppermost.

For example, the number 258 (20⊥12 18) would be written:

    ┌───────┐
    │  ⍟ ⍟  │
    │ ⌹⌹⌹⌹⌹ │     (2+5+5)×20
    │ ⌹⌹⌹⌹⌹ │
    │       │         +
    │  ⍟⍟⍟  │
    │ ⌹⌹⌹⌹⌹ │     (3+5+5+5)×1
    │ ⌹⌹⌹⌹⌹ │
    │ ⌹⌹⌹⌹⌹ │
    └───────┘

The  system  boasted  a Zero (represented by a snail or sea shell pictogram) and
when  used  for date calculations, had a curious irregularity in the third place
(and  only  the  third  place) in that items in this position represented 18×20,
rather  than  20×20.  In  APL terms, this means we use ··· 20 20 18 20 to encode
into Mayan calendrical numbers.

Function mayan's optional left argument selects

    0: regular  ··· 20 20 20 base,
    1: calendar ··· 20 18 20 base (default).

As the principal use of arithmetic was astronomical and calendrical, it is prob-
able  that the 18×20 (=360) irregularity was introduced as a simplification. The
Mayan  calendar  year  had 360 regular days together with 5 extra "null" days in
the short month of Wayeb (see below).

We  should not infer any vagueness about the length of a Mayan year: The Priest-
Astronomers  managed  to calculate Sun, Moon and planet cycles to an astonishing
accuracy; for example, the length of a year was calculated to a precision better
than  we  manage with our Gregorian leap year system, even with its no-it-isn't,
yes-it-is adjustment at 100 and 400 years:

    Modern "accurate" solar year    ·   365.242198 days
    Mayan calculation of solar year ·   365.242    days     (-0.000054% error)
    Gregorian leap year system  ·   ·   365.2425   days     (+0.000083% error)

(
    The Mayan calendar uses the following units of time:

                            days  ×\
    Kin                        1   1    (day)
    Uinal                     20  20    (month)
    Tun                      360  18    (year)
    Katun                  7,200  20    (a "score" of years)
    Baktun               144,000  20
    Piktun             2,880,000  20
    Kalabtun          57,600,000  20
    Kinchiltun     1,152,000,000  20
    Alautun       23,040,000,000  20
    Hablatun     460,800,000,000  20
)

(
    The names of cardinal numbers reveal a vestigial decimal system:

    0 xix im    10 lahun                20 hun kal
    1 hun       11 buluc                40 ca kal
    2 caa       12 lahca                60 ox kal
    3 ox        13 oxlahun              80 can kal
    4 can       14 canlahun            100 hoo kal
    5 hoo       15 hoolahun            120 uac kal
    6 uac       16 uaclahun            140 uuc kal
    7 uuc       17 uuclahun            200 ka hoo kal
    8 uaxac     18 uaxaclahun          400 hun bak
    9 bolon     19 bolonlahun          800 ca bak
                                     1,200 ox bak
                                     1,600 can bak
                                     2,000 hoo bak
                                     8,000 hun pic
                                   160,000 hun calab
                                 3,200,000 hun kinchil
                                64,000,000 hun alau
    (
        The  name  for 10 "lahun" appears to include the word for 1 "hun", which
        means  it  might translate into English as something like "one-ty". This
        would imply that the Maya had distinct words for the numbers 0-9, where-
        as English has distinct words for 1-10 (with Zero following later).

        Mayan months and weeks both start with day 0.

        All of this suggests that the Maya were ⎕IO←0 people.

        Yay Maya!
    )
)

(
    Positional number systems lend themselves to calculation using various types
    of abacus. An example "Nepohualtzitzin" dates from 900-1000 AD.

    See: eval.dws/notes.soroban
)

To convert decimal number 86,672 to (calendrical) Mayan, we would use:

          20 20 18 20⊤86627
    12 0 11 7

Which, using Mayan-style digits, becomes:

     ⍟ ⍟            12 × 7200
    ⌹⌹⌹⌹⌹
    ⌹⌹⌹⌹⌹              +

     _@/             0 × 360        (_@/ is a picture of a snail)
                       +
      ⍟             11 × 20
    ⌹⌹⌹⌹⌹
    ⌹⌹⌹⌹⌹              +

     ⍟ ⍟             7 × 1
    ⌹⌹⌹⌹⌹


Examples:

      mayan 6386            ⍝ (20 18 20⊤6386 → 17 13 6)

  ⍟ ⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

  ⍟⍟⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

   ⍟
 ⌹⌹⌹⌹⌹

      mayan 4321            ⍝ (20 18 20⊤4321 → 12 0 1)

  ⍟ ⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

  _@/

   ⍟

      mayan 70              ⍝ "Three score years and ten".

  ⍟⍟⍟

 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹


      disp∘mayan¨ ⎕         ⍝ various numbers:
⎕:
   1234     2345     3456     4567     5678      360     7200
 ┌─────┐  ┌─────┐  ┌─────┐  ┌─────┐  ┌─────┐  ┌─────┐  ┌─────┐
 │     │  │     │  │     │  │     │  │     │  │     │  │     │
 │ ⍟⍟⍟ │  │  ⍟  │  │⍟⍟⍟⍟ │  │ ⍟ ⍟ │  │⌹⌹⌹⌹⌹│  │  ⍟  │  │  ⍟  │
 ├─────┤  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  ├─────┤  ├─────┤
 │     │  ├─────┤  ├─────┤  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │     │  │     │
 │ ⍟ ⍟ │  │     │  │     │  ├─────┤  ├─────┤  │ _@/ │  │ _@/ │
 │⌹⌹⌹⌹⌹│  │⍟⍟⍟⍟ │  │⌹⌹⌹⌹⌹│  │     │  │     │  ├─────┤  ├─────┤
 ├─────┤  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │ ⍟ ⍟ │  │ ⍟⍟⍟ │  │     │  │     │
 │     │  ├─────┤  ├─────┤  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │ _@/ │  │ _@/ │
 │⍟⍟⍟⍟ │  │     │  │     │  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  └─────┘  ├─────┤
 │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │  ⍟  │  ├─────┤  ├─────┤           │     │
 │⌹⌹⌹⌹⌹│  └─────┘  │⌹⌹⌹⌹⌹│  │     │  │     │           │ _@/ │
 └─────┘           │⌹⌹⌹⌹⌹│  │ ⍟ ⍟ │  │ ⍟⍟⍟ │           └─────┘
                   │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│  │⌹⌹⌹⌹⌹│
                   └─────┘  └─────┘  │⌹⌹⌹⌹⌹│
                                     │⌹⌹⌹⌹⌹│
                                     └─────┘

⍝ The following function converts ⎕TS-style dates into Mayan "Long Count" form,
⍝ assuming that the Long Count epoch started August 11th, 3114 BCE.

      long_count←{      ⍝ Mayan Long Count from Gregorian (⎕TS) date.
          ⍺←584283      ⍝ default GMT correlation: 0.0.0.0.0 ≡ JD:584283.
          G←⌊days ⍵     ⍝ Gregorian day.
          J←2415020+G   ⍝ Julian day.
          mayan J-⍺     ⍝ Mayan from Julian.
      }

      long_count 2003 12 25                     ⍝ 2003-12-25 ≡ 12.19.10.15.16

  ⍟ ⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

 ⍟⍟⍟⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

   ⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

      long_count 2012 12 21     ⍝ First day of 14th Baktun.

  ⍟⍟⍟
 ⌹⌹⌹⌹⌹
 ⌹⌹⌹⌹⌹

  _@/

  _@/

  _@/

  _@/

⍝ This stand-alone version converts a YYYY MM DD vector into the equivalent
⍝ n.n.n.n.n vector:

      long_vec←{          ⍝ Raw long-count vector.
          ⍺←584283        ⍝ default GMT correlation: 0.0.0.0.0 ≡ JD:584283.
          G←⌊days ⍵       ⍝ Gregorian day.
          J←2415020+G     ⍝ Julian day.
          M←J-⍺           ⍝ Mayan from Julian.

          n←1+⌈18⍟1⌈M     ⍝ generous number of digits.
          b←20-2⌽n↑2      ⍝ encoding base.
          v←b⊤M           ⍝ long-count vector.
          (∨\v≠0)/v       ⍝ without leading 0s.
      }

      long_vec 2012 12 21   ⍝ first day of 14th Backtun
13 0 0 0 0

Correlation with Modern Dates
-----------------------------
There  is  overwhelming  evidence  that the Maya maintained a rigorous calendar.
However,  as this ceased with the decline of the civilisation, it has been diff-
icult to determine how Mayan dates correspond to the Julian or Gregorian calend-
ars. Two correlations seem to be favoured:

The first, known as "GMT"  (Goodman, Martinez, Thompson),  suggests  that  Mayan
date 0.0.0.0.0 corresponds to  Julian date 584,283.  This is based on studies of
some  contemporary  Central American communities, whose calendar seems to be in-
herited from the Maya.  The  argument  is  that  (unless  the population of such
peoples dwindled to a critical number at some point in the past before  recover-
ing) it is inconceivable that their calendar should have missed or gained  days;
it would be as unthinkable as western civilisation's  missing  or  duplicating a
couple of Wednesdays.

The second "GMT+2", which uses relatively recent evidence, is  based  upon Mayan
recorded observations  of  eclipses.  We  can  date  such  events  with  extreme
accuracy, and they suggest a correlation with Julian date 584,285.

If the astronomical recording was accurate, an explanation  of  the  discrepency
might be that the 584,285 calendar was subsequently adjusted to realign with the
seasons in the same way the Gregorian calendar skipped 3-13 September in 1752.

The functions shown here use the 584,283 (GMT) correlation, which now appears to
be the more generally accepted one.

Cycles
------
Today  almost  all of the civilised world enjoys a 7-day week. This cycle, which
is  independent of month and year, is so universal that we forget why we decided
upon seven.

(muse:

    There are many suggestions as to the origin of the 7-day week, and no single
    theory is widely accepted as the definitive answer.

    One  example is that the concept of the week arose in primitive agricultural
    societies,  where  seven  days  was about the right interval for a farmer to
    prepare  and  bring  his goods to market. A shorter interval would waste too
    much  time away from production, and a longer one might risk goods perishing
    between market days.

    Note  firstly, that there are strong reasons for market days to occur at ex-
    actly  regular  intervals:  every so-many days, rather than being constantly
    re-negotiated.  With a regular "week", there is much more chance of everyone
    showing up on the same day; a prerequisite for successful trading.

    It  is tempting to speculate whether widespread acceptance of an interval of
    seven days might have come about by a form of natural selection, rather than
    as  a collective or bureaucratic conscious decision: A farmer returning from
    his  local  market might have found on occasion, that his figs, chickens and
    so-forth  were  ready again after six days. If his local market did not fall
    on  the  following  day,  he might have felt inclined to take his goods to a
    neighbouring village's market even though it was slightly farther to travel.

    Villages whose market days just happened to accommodate natural agricultural
    cycles  would  tend to retain regular trade as well as to attract occasional
    additional  visitors,  whereas  those with slightly more inconvenient cycles
    would tend to decline. In this way, farmer-friendly market cycles would tend
    automatically to become the norm.

    (
        Having  established  same-length  cycles in adjacent villages, there may
        have  been  a  second mechanism that selected for staggered market days,
        while reinforcing their regularity.

        Service  providers  such as pot-menders and tooth-pullers, who needed no
        time  to prepare between market days, would probably have toured markets
        on  different  days in nearby locations. In the case of a collision, the
        trader  would  probably  have chosen the better-attended market, and his
        presence  there  would in turn have made that market marginally more at-
        tractive to shoppers, tending to increase its size, ... and so on.

        Looking  at  the  larger picture, these rotating service providers (axe-
        grinders,  sooth-sayers,  hair-cutters, entertainers, ...) could be seen
        as  the teeth on the interlocking cogs of an expanding economic machine,
        which  absorbed  adjacent communities, synchronising them into the 7-day
        cycle.

        (
            If  this were the case, we might expect the names of the days of the
            week  (in a particular locale) to indicate the locations of the more
            important  markets in that area: "Oxford-day", "Banbury-day", and so
            forth, rather than being named after deities.
        )
    )

    That  the Mayan civilization chose a week with thirteen days (see below), as
    opposed to one with seven, does not, of itself, detract from this theory, as
    the  Mayan  agricultural  profile was quite different from that of Eurasia's
    "Fertile Crescent".  See "Guns, Germs, and Steel: The Fates of Human Societ-
    ies", Jared Diamond.

    But all of this is merely conjecture ...
)

The  Mayan calendar included several cycles, two of which often accompany a Long
Count date. Combinations such as these are similar to our compound date format:

    Wednesday, November 5, 2003.
    │          │
    │          └──── Month  12-cycle.
    └─────────────── Weekday 7-cycle.

    "Haab"    is a cycle of 18 × 20-day months.
    "Tzolkin" is a cycle of 20 × 13-day weeks.

Haab  has 18 × 20-day months together with one 5-day month making a total of 365
days in the year:

    Pop         Wo          Sip         Sotz'       Tzek
    Xul         Yaxk'in     Mol         Ch'en       Yax
    Sak         Keh         Mak         K'ank'in    Muwan
    Pax         K'ayab      Kumk'u      Wayeb (5)

    Months←'Pop' 'Wo' 'Sip' 'Sotz''' 'Tzek' 'Xul' 'Yaxk''in' 'Mol' 'Ch''en' 'Yax' 'Sak' 'Keh' 'Mak' 'K''ank''in' 'Muwan' 'Pax' 'K''ayab' 'Kumk''u' 'Wayeb'

The  short month of Wayeb is inauspicious; one should refrain from washing, hair
combing and nit-picking during Wayeb.

Day-within-month and Month name can be extracted by:

      haab←{⎕IO←0                       ⍝ Mayan day within month.
          ⍺←245                         ⍝ align Gregorian and Maya cycles.
          mon day←0 20⊤365|⍺+⌊days ⍵    ⍝ month index and day number.
          name←mon⊃Months               ⍝ name of month.
          day name                      ⍝ origin-0 day within month.
      }

      haab 2003 12 25   ⍝ Christmas day 2003 fell on the fourth day of K'ank'in.
4  K'ank'in

      haab 2003 12 26   ⍝ Boxing day fell on the fifth day of K'ank'in.
5  K'ank'in

      haab 2003 12 27   ⍝ ... etc.
6  K'ank'in

The names of the 20 Tzolkin days are as follows:

    Imix        Ik'         Ak'bal      K'an        Chikchan
    Kimi        Manik'      Lamat       Muluk       Ok
    Chuwen      Eb          Ben         Ix          Men
    Kib         Kaban       Etz'nab     Kawak       Ahaw

    Days←'Imix' 'Ik''' 'Ak''bal' 'K''an' 'Chikchan' 'Kimi' 'Manik''' 'Lamat' 'Muluk' 'Ok' 'Chuwen' 'Eb' 'Ben' 'Ix' 'Men' 'Kib' 'Kaban' 'Etz''nab' 'Kawak' 'Ahaw'

The  20  Tzolkin  days  are  reused cyclically for successive 13-day weeks. This
means  that  a particular day number (0-12) coincides with a particular day name
(Imix-Ahaw) only every 20×13 = 260 days.

The Tzolkin date can be extracted using:

      tzolkin←{⎕IO←0                ⍝ Mayan Tzolkin number and day.
          ⍺←2 16                    ⍝ align Gregorian and Maya cycles.
          num day←13 20|⍺+⌊days ⍵   ⍝ day number and name index.
          name←day⊃Days             ⍝ day name.
          (num+1)name               ⍝ origin-1 day within cycle.
      }

      tzolkin 2003 12 25    ⍝ Christmas day 2003 fell on day 9, a Kib-day.
9  Kib

      tzolkin 2003 12 26    ⍝ Boxing day fell on day 10, a Kaban-day.
10  Kaban

      tzolkin 2003 12 27    ⍝ ... etc.
11  Etz'nab

An Attractive Gift
------------------
Print  the result of the following function on a stone tablet or gold pendant to
make an attractive "Stela" of a loved one's date of birth. The final (lower) two
digits  show  Tzolkin and Haab dates, the Mayan cultural equivalent of an astro-
logical star sign.

      time_units←'Kin' 'Uinal' 'Tun' 'Katun' 'Baktun' 'Piktun' 'Kalabtun' 'Kinchiltun' 'Alautun' 'Hablatun'

      stela←{                               ⍝ Stela for date ⍵ (yyyy mm dd).
          long←long_count ⍵                 ⍝ Long Count days.
          hnum hname←haab ⍵                 ⍝ month and day.
          tnum tname←tzolkin ⍵              ⍝ week and day.
          digits←long⍪↑,∘mayan¨tnum hnum    ⍝ maya-style digits.
          lft←1 0∘↓¨digits                  ⍝ left-side column: numbers.
          rgt←⌽7↑hname tname,time_units     ⍝ right-side column: names.
          disp lft,rgt                      ⍝ collected stela.
      }

Here  are  Stelae for Victoria and David Beckham, together with little Brooklyn,
Romeo, Cruz and Harper. Notice how Brooklyn and Cruz share the same star signs.

         david←1974 04 17
      victoria←1975 05 02
      brooklyn←1999 03 04
         romeo←2002 09 01
          cruz←2005 02 20
       harper7←2011 07 10

      stela¨¨(david victoria)(brooklyn romeo cruz harper7)
  ┌─────┬──────┐  ┌─────┬──────┐    ┌─────┬──────┐  ┌─────┬──────┐  ┌─────┬──────┐  ┌─────┬──────┐
  │ ⍟ ⍟ │      │  │ ⍟ ⍟ │      │    │ ⍟ ⍟ │      │  │ ⍟ ⍟ │      │  │ ⍟ ⍟ │      │  │ ⍟ ⍟ │      │
  │⌹⌹⌹⌹⌹│Baktun│  │⌹⌹⌹⌹⌹│Baktun│    │⌹⌹⌹⌹⌹│Baktun│  │⌹⌹⌹⌹⌹│Baktun│  │⌹⌹⌹⌹⌹│Baktun│  │⌹⌹⌹⌹⌹│Baktun│
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │
  ├─────┼──────┤  ├─────┼──────┤    ├─────┼──────┤  ├─────┼──────┤  ├─────┼──────┤  ├─────┼──────┤
  │ ⍟⍟⍟ │      │  │ ⍟⍟⍟ │      │    │⍟⍟⍟⍟ │      │  │⍟⍟⍟⍟ │      │  │⍟⍟⍟⍟ │      │  │⍟⍟⍟⍟ │      │
  │⌹⌹⌹⌹⌹│Katun │  │⌹⌹⌹⌹⌹│Katun │    │⌹⌹⌹⌹⌹│Katun │  │⌹⌹⌹⌹⌹│Katun │  │⌹⌹⌹⌹⌹│Katun │  │⌹⌹⌹⌹⌹│Katun │
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │
  ├─────┼──────┤  ├─────┼──────┤    ├─────┼──────┤  ├─────┼──────┤  ├─────┼──────┤  ├─────┼──────┤
  │ _@/ │ Tun  │  │  ⍟  │ Tun  │    │⌹⌹⌹⌹⌹│ Tun  │  │⍟⍟⍟⍟ │ Tun  │  │ ⍟ ⍟ │      │  │ ⍟⍟⍟ │      │
  ├─────┼──────┤  ├─────┼──────┤    ├─────┼──────┤  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│ Tun  │  │⌹⌹⌹⌹⌹│ Tun  │
  │ ⍟⍟⍟ │      │  │⍟⍟⍟⍟ │      │    │ ⍟ ⍟ │      │  ├─────┼──────┤  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │
  │⌹⌹⌹⌹⌹│Uinal │  │⌹⌹⌹⌹⌹│Uinal │    │⌹⌹⌹⌹⌹│Uinal │  │⍟⍟⍟⍟ │Uinal │  ├─────┼──────┤  │⌹⌹⌹⌹⌹│      │
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │ _@/ │Uinal │  ├─────┼──────┤
  ├─────┼──────┤  ├─────┼──────┤    │⌹⌹⌹⌹⌹│      │  ├─────┼──────┤  ├─────┼──────┤  │⍟⍟⍟⍟ │Uinal │
  │ ⍟ ⍟ │      │  │ ⍟ ⍟ │      │    ├─────┼──────┤  │  ⍟  │      │  │⍟⍟⍟⍟ │      │  │⌹⌹⌹⌹⌹│      │
  │⌹⌹⌹⌹⌹│ Kin  │  │⌹⌹⌹⌹⌹│ Kin  │    │⍟⍟⍟⍟ │      │  │⌹⌹⌹⌹⌹│ Kin  │  │⌹⌹⌹⌹⌹│ Kin  │  ├─────┼──────┤
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    │⌹⌹⌹⌹⌹│ Kin  │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│ Kin  │
  ├─────┼──────┤  ├─────┼──────┤    │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │
  │ ⍟ ⍟ │  Eb  │  │⌹⌹⌹⌹⌹│  Eb  │    │⌹⌹⌹⌹⌹│      │  ├─────┼──────┤  ├─────┼──────┤  ├─────┼──────┤
  │⌹⌹⌹⌹⌹│      │  │⌹⌹⌹⌹⌹│      │    ├─────┼──────┤  │⌹⌹⌹⌹⌹│ Kib  │  │ ⍟⍟⍟ │Kawak │  │ ⍟ ⍟ │  Ok  │
  ├─────┼──────┤  ├─────┼──────┤    │ ⍟ ⍟ │Kawak │  │⌹⌹⌹⌹⌹│      │  ├─────┼──────┤  │⌹⌹⌹⌹⌹│      │
  │⌹⌹⌹⌹⌹│ Pop  │  │ _@/ │  Wo  │    │⌹⌹⌹⌹⌹│      │  ├─────┼──────┤  │ ⍟ ⍟ │K'ayab│  ├─────┼──────┤
  └─────┴──────┘  └─────┴──────┘    ├─────┼──────┤  │⍟⍟⍟⍟ │ Mol  │  └─────┴──────┘  │ ⍟⍟⍟ │      │
                                    │ ⍟ ⍟ │      │  │⌹⌹⌹⌹⌹│      │                  │⌹⌹⌹⌹⌹│ Tzek │
                                    │⌹⌹⌹⌹⌹│K'ayab│  └─────┴──────┘                  │⌹⌹⌹⌹⌹│      │
                                    │⌹⌹⌹⌹⌹│      │                                  │⌹⌹⌹⌹⌹│      │
                                    └─────┴──────┘                                  └─────┴──────┘
References:
    http://en.wikipedia.org/wiki/Maya_numerals
    http://en.wikipedia.org/wiki/Mesoamerican_Long_Count_calendar
    Ifrah, G. "The Universal History of Numbers".
    Diamond, J. "Guns, Germs, and Steel: The Fates of Human Societies".
    http://mayan-calendar.com/calc.html

See also: eval.dws/notes.soroban.
See also: roman days Dates ary

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