

  The Roman number system, unlike our current notational system, is  a so-
  called addition system.  With a notational system the magnitude of a di-
  git depends also on their position within the number  (e.g. 3531 = digit
  3 once has magnitude 3000 and once has magnitude 30).  Instead, each di-
  git has  the same  magnitude in an addition system, independent of where
  it occurs within the number.  In both kind of systems,  however, the ma-
  gnitude of the number is determined from the addition  of the magnitudes
  of all the digits that make it up.  In the Roman system, actually, there
  is an exception whereby certain  digit occurrences are in fact  subtrac-
  tive (later designated as subtractive combination).  This was introduced
  only later for simplification and was originally not a component of this
  number system.

  The following indications with the associated values are defined:

  Basic character (BC)     Auxiliary character (AC)
  Indication  Magnitude    Indication    Magnitude
   I           1            V             5
   X           10           L             50
   C           100          D             500
   M           1000

  When reading and writing Roman number words, the following rules apply.

  1. The basic unit of a  Roman number word will be  called "Roman  number
     character" RC here.  A Roman number  word consists  after a lining up
     of RC.

     e.g.: Roman number word MMDIX consists of 4 RC: "M", "M", "D", "IX"

  2. A RC is either a basic character  BC, an auxiliary  character AC or a
     "subtractive combination" SC (definition given by rule 7).

     e.g.: MMDIX consists of the following RC : "M" = BC, "M" = BC, "D" =
           AC, "IX" = SC

  3. Each RC has a defined magnitude.  The magnitude of a BC  or AC is in-
     dicated in  the above table.  For SC the magnitude is  to be inferred
     from rule 7.

     e.g.: magnitude of AC "V" is 5
     e.g.: magnitude of SC "IV" is 4

  4. In a Roman  number word the  individual RCs are arranged so that they
     have descending magnitude.

     e.g.: MDCCXIII (M > D > C > X > I)

  5. The  magnitude of a Roman number word is given by  the sum of the va-
     lues of the individual RCs

     e.g.: MDVII = 1000 + 500 + 5 + 1 + 1 = 1507

  6. The same AC may be repeated at most once;  a BC may appear only  once
     if it is  used as the  leftmost indication of a SC, otherwise  it may
     appear three times.

     e.g.: 66 is not XXXXXXIIIIII but LXVI
     e.g.: IVIV or VV or VIV is not allowed 

  7. A  SC consists  of 2 indications, so that a BC is to the left of a BC 
     or AC of larger  magnitude.  The  magnitude of  a SC  is given by the 
     magnitude of the right BC/AC minus the magnitude of the left BC.

     Special rule:
     I stands only before V and X
     X stands only before L and C
     C stands only before D and M

     e.g.: IV = 5-1 = 4

  In the following  table for illustration  examples of Roman  numbers are
  represented:

  Decimal   Roman   Decimal   Roman   Decimal   Roman
  1         I       11        XI      70        LXX
  2         II      12        XII     80        LXXX
  3         III     13        XIII    90        XC
  4         IV      ...       ...     98        XCVIII
  5         V       19        XIX     99        XCVIV
  6         VI      20        XX      100       C
  7         VII     30        XXX     110       CX
  8         VIII    40        XL      200       CC
  9         IX      50        L       999       CMXCIX
  10        X       60        LX      1000      M


  Now, it is very easy  to convert any number  (less than 4000) into roman
  notation. Just find the maximum RC in the number, subtract its magnitude
  and find the next maximum until the number reaches 0. 
