## Combination functions

Function: int gsl_combination_next (gsl_combination * c)
  This function advances the combination c to the next combination in lexicographic order and returns `GSL_SUCCESS`. If no further combinations are available it returns `GSL_FAILURE` and leaves c unmodified. Starting with the fisrst combination and repeatedly applying this function will iterate through all possible combinations of a given order.

Function: int gsl_combination_prev (gsl_combination * c)
  This function steps backwards from the combination c to the previous combination in lexicographic order, returning `GSL_SUCCESS`. If no previous combination is available it returns `GSL_FAILURE` and leaves c unmodified.