between -a (ulong x, ulong left, ulong right)
{
  return () {
              if (left < x < right) 
              {
                return 1;
              }
              else
              {
                if (x == left | x == right)
                {
                  return 0;
                }
                else
                {
                  error (ERR_BOUNDS);
                }
              }
            };
}