anchor.diff:          !        sym = sym_index,
           !        U = U,
           !        t = t,
  -        !        ktwist = {...},    -- D-dimensional vector.
  +        !        twist = {...},    -- D-dimensional vector.
           !    }
   
           use, intrinsic :: iso_c_binding, only: c_ptr, c_int, c_loc
  
positive.code:         integer :: err
  
          character(10), parameter :: keys(10) = [character(10) :: 'sys', 'cutoff', 'dim', 'rs', 'nel', 'electrons', &
                                                 'ms', 'sym', 'ktwist', 'chem_pot']
  
          lua_state = flu_copyptr(L)
          call get_sys_t(lua_state, sys, new)
  
negative.code:         logical :: new, new_basis
          integer :: err
          character(10), parameter :: keys(9) = [character(10) :: 'sys', 'nel', 'electrons', 'lattice', 'U', 't', &
                                                                  'ms', 'sym', 'twist']
  
          lua_state = flu_copyptr(L)
          call get_sys_t(lua_state, sys, new)
  