; formalities
 input-roman = number / letter
 number      = c-0 / c-1 / c-2 / c-3 / c-4 / c-5 / c-6 / c-7 / c-8 / c-9
 letter      = c-a / c-b / c-c / c-d / c-e / c-f / c-g / c-h / c-i / c-j
                   / c-k / c-l / c-m / c-n / c-o / c-p / c-q / c-r / c-s
                   / c-t / c-u / c-v / c-w / c-x / c-y / c-z

 ; possible sources of mistranscribed numbers
 c-0 = "O" / "6" / "D" / "G"
 c-1 = "I" / "L" / "7" / "2" / "Z"
 c-2 = "Z" / "7" / "P" / "E" / "1"
 c-3 = "8" / "B"
 c-4 = "G" / "U"
 c-5 = "S" / "7"
 c-6 = "0" / "O" / "8" / "G" / "C" / "B" / "D"
 c-7 = "J" / "I" / "1" / "L"
 c-8 = "B" / "3" / "6"
 c-9 = "G" / "Y" / "O" / "0" / "D"

 ; possible sources of mistranscribed letters
 c-a = "G" / "Q" / "O" / "0"
 c-b = "6" / "3" / "8" / "P" / "0" / "O"
 c-c = "R" / "6" / "I" / "L" / "O" / "0"
 c-d = "0" / "O" / "9" / "Q" / "G" / "6" / "A"
 c-e = "F" / "G" / "0" / "2" / "K" / "Z" / "S" / "O"
 c-f = "E" / "K" / "T" / "P" / "Y" / "4" / "B" / "7" / "1"
 c-g = "9" / "Q" / "8" / "6" / "0" / "C" / "4" / "O"
 c-h = "B" / "N" / "A" / "4" / "6" / "M" / "W" / "F" / "R" / "T" / "X"
 c-i = "1" / "L" / "7" / "J" / "2" / "T" / "Z"
 c-j = "I" / "7" / "2" / "9" / "1" / "U" / "T" / "Q" / "P" / "Y" / "Z"
           / "L" / "S"
 c-k = "F" / "X" / "H" / "R" 
 c-l = "1" / "2" / "7" / "C" / "I" / "J" / "R" / "T" / "Y" / "Z"
 c-m = "H" / "8" / "E" / "3" / "N" / "V" / "W" 
 c-n = "H" / "R" / "C" / "2" / "4" / "M" / "O" / "P" / "K" / "T" / "Z"
 c-o = "0" / "6" / "9" / "A" / "D" / "G" / "C" / "E" / "B" / "N" / "P"
           / "Q" / "R"
 c-p = "F" / "4" / "8" / "2" / "B" / "J" / "R" / "N" / "O" / "T" / "Y"
 c-q = "O" / "G" / "9" / "Y" / "1" / "7" / "L"
 c-r = "K" / "B" / "V" / "C" / "1" / "L" / "2"
 c-s = "5" / "6" / "9" / "B" / "G" / "Q" / "A" / "Y"
 c-t = "1" / "4" / "7" / "F" / "I" / "J" / "L" / "P" / "X" / "Y"
 c-u = "V" / "N" / "A" / "4" / "9" / "W" / "Y"
 c-v = "U" / "R" / "N"
 c-w = "M" / "N" / "U" / "V"
 c-x = "K" / "F" / "4" / "T" / "V" / "Y"
 c-y = "G" / "V" / "J" / "I" / "4" / "9" / "T" / "F" / "Q" / "1"
 c-z = "2" / "1" / "L" / "R" / "I" / "7" / "V" / "3" / "4"