anchor.diff:          if (sys%momentum_space .or. sys%system == read_in) then
               if (sys%real_lattice%finite_cluster) call stop_all(this,'"finite" keyword only valid for calculations in real-space.')
           end if
  -        
  +
           if (sys%system == ringium .and. sys%ringium%radius < depsilon) call stop_all(this, 'Ringium must have a positive radius.')
  -
   
       end subroutine check_sys
   
  
positive.code:             call stop_all(this, 'metropolis_attempts must be greater than zero.')
          end if
  
      end subroutine check_dmqmc_opts
  
      subroutine check_ccmc_opts(ccmc_in)
  
negative.code:                 'Flipping the reference state will give a state which has a different value of Ms and so cannot be used here.')
          end if
  
          if (sys%symmetry < 0) call stop_all(this, 'symmetry must be greater than zero')
  
      end subroutine check_fciqmc_opts
  
      subroutine check_qmc_opts(qmc_in, simple_fciqmc)
  