### 9.4 Permutation properties

Function: size_t gsl_permutation_size (const gsl_permutation * p)

  This function returns the size of the permutation p.

Function: size_t * gsl_permutation_data (const gsl_permutation * p)

  This function returns a pointer to the array of elements in the permutation p.

Function: int gsl_permutation_valid (const gsl_permutation * p)

  This function checks that the permutation p is valid. The n elements should contain each of the numbers 0 to n-1 once and only once.