code: def _crossover_a_pair(chromosome_1, chromosome_2, mask):
          
  
          for _idx in range(len(chromosome_1)):
  
              if mask[_idx] == 1:
                  # Swap values
                  chromosome_1[_idx], chromosome_2[_idx] = chromosome_2[_idx], chromosome_1[_idx]
docs: !
          @brief Crossovers a pair of chromosomes.
          
          @param[in] chromosome_1 (numpy.array): The first chromosome for crossover.
          @param[in] chromosome_2 (numpy.array): The second chromosome for crossover.
          @param[in] mask (numpy.array): Crossover mask that defines which genes should be swapped.