anchor.diff:          use checking, only: check_allocate
           use utils, only: binom_i
           use utils, only: get_free_unit, int_fmt
  +        use calc, only: doing_calc, exact_diag, lanczos_diag
   
           integer :: i, bit_pos, bit_element, ierr
           character(4) :: fmt1(5)
  
positive.code:             fmt1 = int_fmt((/nel, nbasis, tot_ndets, i0_length, basis_length/), padding=1)
              write (6,'(1X,a20,'//fmt1(1)//')') 'Number of electrons:', nel
              write (6,'(1X,a26,'//fmt1(2)//')') 'Number of basis functions:', nbasis
              write (6,'(1X,a32,'//fmt1(3)//')') 'Total size of determinant space:', tot_ndets
              write (6,'(1X,a61,'//fmt1(4)//',/)') 'Bit-length of integers used to store determinant bit-strings:', i0_length
              write (6,'(1X,a57,'//fmt1(5)//',/)') 'Number of integers used to store determinant bit-strings:', basis_length
          end if
  
negative.code: ! the desired spin and momentum symmetry.
  integer :: ndets
  
  ! Total (exact) size of determinant space.
  ! Only used in FCI calculations, where we can be certain that we have fewer
  ! determinants than 2**31-1 (ie no overflow).
  ! Whilst it's set (and frequently overflows) in FCIQMC calculations, we never
  ! actually use it then.  See the estimate_hilbert_space option to obtain an
  ! estimate estimate (or, in real-space systems, exact to a certain precision)
  ! for the size of the Hilbert space for a given symmetry which avoids overflows.
  integer :: tot_ndets
  
  ! Number of determinants of each symmetry.
  