anchor.diff:      IMPLICIT NONE
       TYPE(QuTree), POINTER       :: qA,qB,qC
       REAL(DOUBLE),OPTIONAL       :: tolerance
  -    REAL(DOUBLE)                :: Saved_tolerance,norm,TrueError,fricnfrac
  +    REAL(DOUBLE)                :: Saved_tolerance,norm,AbsError,RelError,TargetError,ABNorm
       INTEGER                     :: SpAMM_count
       REAL(DOUBLE),ALLOCATABLE,DIMENSION(:,:) :: dA,dB,dC
  -
   
       IF(PRESENT(tolerance))THEN
          Saved_tolerance=SpAMM_tolerance
  
positive.code:     ! Associated
      IF(ASSOCIATED(qA).AND.ASSOCIATED(qB))THEN
      ! Bounds
      IF(qA%Norm*qB%Norm*8D0**(HALF*DBLE(qA%Lev))<SpAMM_tolerance)RETURN
      ! Allocate
      IF(.NOT.ASSOCIATED(qC))CALL NewQuNode(qC,count=count)
      ! Boxing
  
negative.code:     qC%Lev=qA%Lev
      qC%Box=qA%Box
      qC%Norm=qA%Norm
      IF(qA%Siz==SpAMM_BLOCK_SIZE.AND.ALLOCATED(qA%Blok))THEN
         IF(.NOT.ALLOCATED(qC%Blok)) &
            ALLOCATE(qC%Blok(1:SpAMM_BLOCK_SIZE,1:SpAMM_BLOCK_SIZE))
  