anchor.diff:               (space-6 (~ (1+ start-1) 2 end-1 ~ (1+ start-2) 2 end-2 ~ start-3 2 end-3))
                (space-7 (~ (1+ start-1) 2 end-1 ~ (1+ start-2) 2 end-2 ~ (1+ start-3) 2 end-3)))
            (fuse u*
  -               (α #'* 0.5d0
  +               (α #'* 1/2
                     (α #'+
                        (reshape u* (τ (i j k) ((1+ i) j k)) space-1)
                        (reshape u* (τ (i j k) ((1- i) j k)) space-1)))
  -               (α #'* 0.5d0
  +               (α #'* 1/2
                     (α #'+
                        (reshape u* (τ (i j k) (i (1+ j) k)) space-2)
                        (reshape u* (τ (i j k) (i (1- j) k)) space-2)))
  -               (α #'* 0.5d0
  +               (α #'* 1/2
                     (α #'+
                        (reshape u* (τ (i j k) (i j (1+ k))) space-3)
                        (reshape u* (τ (i j k) (i j (1- k))) space-3)))
  -               (α #'* 0.25d0
  +               (α #'* 1/4
                     (α #'+
                        (reshape u* (τ (i j k) (i (1+ j) (1+ k))) space-4)
                        (reshape u* (τ (i j k) (i (1+ j) (1- k))) space-4)
                        (reshape u* (τ (i j k) (i (1- j) (1+ k))) space-4)
                        (reshape u* (τ (i j k) (i (1- j) (1- k))) space-4)))
  -               (α #'* 0.25d0
  +               (α #'* 1/4
                     (α #'+
                        (reshape u* (τ (i j k) ((1+ i) j (1+ k))) space-5)
                        (reshape u* (τ (i j k) ((1+ i) j (1- k))) space-5)
                        (reshape u* (τ (i j k) ((1- i) j (1+ k))) space-5)
                        (reshape u* (τ (i j k) ((1- i) j (1- k))) space-5)))
  -               (α #'* 0.25d0
  +               (α #'* 1/4
                     (α #'+
                        (reshape u* (τ (i j k) ((1+ i) (1+ j) k)) space-6)
                        (reshape u* (τ (i j k) ((1+ i) (1- j) k)) space-6)
                        (reshape u* (τ (i j k) ((1- i) (1+ j) k)) space-6)
                        (reshape u* (τ (i j k) ((1- i) (1- j) k)) space-6)))
  -               (α #'* 0.125d0
  +               (α #'* 1/8
                     (α #'+
                        (reshape u* (τ (i j k) ((1+ i) (1+ j) (1+ k))) space-7)
                        (reshape u* (τ (i j k) ((1+ i) (1+ j) (1- k))) space-7)
  
positive.code:              (space-2 (~ start-1 2 end-1 ~ (1+ start-2) 2 end-2))
               (space-3 (~ (1+ start-1) 2 end-1 ~ (1+ start-2) 2 end-2)))
           (fuse u*
                 (α #'* 0.5d0
                    (α #'+
                       (reshape u* (τ (i j) ((1+ i) j)) space-1)
                       (reshape u* (τ (i j) ((1- i) j)) space-1)))
                 (α #'* 0.5d0
                    (α #'+
                       (reshape u* (τ (i j) (i (1+ j))) space-2)
                       (reshape u* (τ (i j) (i (1- j))) space-2)))
                 (α #'* 0.25d0
                    (α #'+
                       (reshape u* (τ (i j) ((1+ i) (1+ j))) space-3)
                       (reshape u* (τ (i j) ((1+ i) (1- j))) space-3)
  
negative.code:         (fuse*
           (reshape u selection)
           (α #'+
              (α #'* 1/8
                 (reshape u interior))
              (α #'* 1/16
                 (reshape u (τ (i j k) ((1+ i) j k)) interior)
                 (reshape u (τ (i j k) (i (1+ j) k)) interior)
                 (reshape u (τ (i j k) (i j (1+ k))) interior)
                 (reshape u (τ (i j k) ((1- i) j k)) interior)
                 (reshape u (τ (i j k) (i (1- j) k)) interior)
                 (reshape u (τ (i j k) (i j (1- k))) interior))
              (α #'* 1/32
                 (reshape u (τ (i j k) (i (1+ j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1+ i) j (1+ k))) interior)
                 (reshape u (τ (i j k) ((1+ i) (1+ j) k)) interior)
                 (reshape u (τ (i j k) (i (1- j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1- i) j (1+ k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1+ j) k)) interior)
                 (reshape u (τ (i j k) (i (1+ j) (1- k))) interior)
                 (reshape u (τ (i j k) ((1+ i) j (1- k))) interior)
                 (reshape u (τ (i j k) ((1+ i) (1- j) k)) interior)
                 (reshape u (τ (i j k) (i (1- j) (1- k))) interior)
                 (reshape u (τ (i j k) ((1- i) j (1- k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1- j) k)) interior))
              (α #'* 1/64
                 (reshape u (τ (i j k) ((1+ i) (1+ j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1+ i) (1+ j) (1- k))) interior)
                 (reshape u (τ (i j k) ((1+ i) (1- j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1+ i) (1- j) (1- k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1+ j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1+ j) (1- k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1- j) (1+ k))) interior)
                 (reshape u (τ (i j k) ((1- i) (1- j) (1- k))) interior))))
          (τ (i j k) ((+ start-1 (/ (- i start-1) 2))
                      (+ start-2 (/ (- j start-2) 2))
                      (+ start-3 (/ (- k start-3) 2)))))))))
  