// type of compare function for list sort operation (as in 'qsort'): it should
// return a negative value, 0 or positive value if the first element is less
// than, equal or greater than the second
// type of compare function for list sort operation (as in 'qsort'): it should
// return a negative value, 0 or positive value if the first element is less
// than, equal or greater than the second