anchor.diff:      integer(c_long),allocatable::oid(:) !< octal ids
       integer,allocatable::lvl(:) !< tree levels
       integer,allocatable::neib(:,:) !< neighbor lists
  +    integer,allocatable::flag(:) !< flag (0-out, 1-in, 2-cut)
     contains
       procedure,public::init=>initOtGrid
       procedure,public::clear=>clearOtGrid
  
positive.code:   integer,parameter::DIMS=3 !< dimensions
    integer,parameter::N_FACE=6 !< number of faces per cell
    
    !> octree grid
    type,public::otGrid
      ! basic data
  
negative.code:     if(allocated(this%oid)) deallocate(this%oid)
      if(allocated(this%lvl)) deallocate(this%lvl)
      if(allocated(this%neib)) deallocate(this%neib)
      if(allocated(this%flag)) deallocate(this%flag)
    end subroutine
    
    !> position of cell k
  