anchor.diff:      ! Current number of walkers stored in the main list (processor dependent).
       ! This is updated during annihilation and merging of the spawned walkers into
       ! the main list.
  +    ! [review] - FDM: rename (ndets perhaps)? Should this be here?
       integer :: tot_walkers
       ! Total number of particles on all walkers/determinants (processor dependent)
       ! Updated during death and annihilation and merging.
  
positive.code:     ! Population above which a determinant is an initiator.
      real(p) :: initiator_population = 3.0_p
  end type initiator_t
  
  ! Array to hold the indices of deterministic states in the dets array, accessed
  ! by calculating a hash value. This type is used by the semi_stoch_t type and
  
negative.code: 
  use const
  use spawn_data
  
  ! [review] - FDM: I think some or all of the following should be in calc.
  
  ! Don't bother renormalising generation probabilities; instead allow forbidden
  ! excitations to be generated and then rejected.
  