anchor.diff:  
           ! In:
           !   sys: information on system under consideration.
  -        !   qs: qmc_state_t derived type with information on
  -        !       current calculation.
           !   logging_info: information on current logging settings.
           !   weighted_sampling: stores sampling weights information when using
           !       importance sampling.
  
positive.code:         use spawn_data, only: spawn_t
  
          type(sys_t), intent(in) :: sys
          type(qmc_state_t), intent(in) :: qs
          type(logging_t), intent(in) :: logging_info
          type(det_info_t), intent(in) :: cdet1, cdet2
          integer, intent(in) :: nattempts_current_det, ireplica
  
negative.code:         !       symmetrically.
          ! In/Out:
          !   rng: random number generator.
          !   qs: qmc_state_t derived type with information on
          !       current calculation. In/Out for compatibility with the
          !       Power-Pitzer excitation generators (not used for DMQMC).
          !   bloom_stats: information on blooms during calculation.
          !   spawn: stored information on spawning.
  
  