 -- string: chr (CODE : int)
     Return the one character long string containing the character which code is CODE.  If CODE does not belong to the range [0..255], raise a runtime error: chr: character out of range.

 -- string: concat (FIRST: string, SECOND: string)

 -- void: exit (STATUS: int)
     Exit the program with exit code STATUS.

 -- void: flush ()

 -- string: getchar ()

 -- int: not (BOOLEAN: int)

 -- int: ord (STRING: string)

 -- void: print (STRING: string)

 -- void: print_int (INT: int)
     Note: this is an EPITA extension.  Output INT in its decimal canonical form (equivalent to %d for printf).

 -- int: size (STRING: string)

 -- string: substring (STRING: string, FIRST: int, LENGTH: int)
     Return a string composed of the characters of STRING starting at the FIRST character (0 being the origin), and composed of LENGTH characters (i.e., up to and including the character FIRST + LENGTH).

     Let SIZE be the size of the STRING, the following assertions must hold:

       * 0 <= FIRST

       * 0 <= LENGTH

       * FIRST + LENGTH <= SIZE

     otherwise a runtime failure is raised: substring: arguments out of bounds.