F mod97(numberstring)
   V segstart = 0
   V step = 9
   V prepended = ‘’
   V number = 0
   L segstart < numberstring.len - step
      number = Int(prepended‘’numberstring[segstart .< segstart + step])
      V remainder = number % 97
      prepended = String(remainder)
      I remainder < 10
         prepended = ‘0’prepended
      segstart += step
      step = 7
   number = Int(prepended‘’numberstring[segstart ..])
   R number % 97

V country2length = [‘IS’ = 26, ‘IT’ = 27, ‘MT’ = 31, ‘MU’ = 30, ‘MR’ = 27, ‘MK’ = 19, ‘IE’ = 22, ‘MD’ = 24,
                    ‘ME’ = 22, ‘MC’ = 27, ‘IL’ = 23, ‘DE’ = 22, ‘DO’ = 28, ‘DK’ = 18, ‘PK’ = 24, ‘HR’ = 21,
                    ‘HU’ = 28, ‘FI’ = 18, ‘LU’ = 20, ‘LT’ = 20, ‘LV’ = 21, ‘KW’ = 30, ‘LI’ = 21, ‘PS’ = 29,
                    ‘PT’ = 25, ‘LB’ = 28, ‘GB’ = 22, ‘GE’ = 22, ‘CR’ = 21, ‘TR’ = 26, ‘GI’ = 23, ‘GL’ = 18,
                    ‘CY’ = 28, ‘CZ’ = 24, ‘GR’ = 27, ‘GT’ = 28, ‘KZ’ = 20, ‘TN’ = 24, ‘CH’ = 21, ‘SE’ = 24,
                    ‘SA’ = 24, ‘SM’ = 27, ‘SI’ = 19, ‘SK’ = 24, ‘PL’ = 28, ‘BR’ = 29, ‘FR’ = 27, ‘FO’ = 18,
                    ‘BA’ = 20, ‘BG’ = 22, ‘BE’ = 16, ‘BH’ = 22, ‘VG’ = 24, ‘RO’ = 24, ‘RS’ = 22, ‘NO’ = 15,
                    ‘NL’ = 18, ‘AZ’ = 28, ‘EE’ = 20, ‘AT’ = 20, ‘ES’ = 24, ‘AL’ = 28, ‘AD’ = 24, ‘AE’ = 23]

F valid_iban(iban_)
   V iban = iban_.replace(‘ ’, ‘’).replace("\t", ‘’)
   I !re:‘[\dA-Z]+’.match(iban)
      R 0B

   I iban.len != :country2length[iban[0.<2]]
      R 0B

   iban = iban[4..]‘’iban[0.<4]
   R mod97(iban.map(ch -> String(Int(ch, radix' 36))).join(‘’)) == 1

L(account) [‘GB82 WEST 1234 5698 7654 32’,
            ‘GB82 TEST 1234 5698 7654 32’]
   print(‘#. validation is: #.’.format(account, valid_iban(account)))