anchor.diff:               (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 #'* 1/2
                     (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 #'* 1/2
                     (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 #'* 1/4
                     (α #'+
                        (reshape u* (τ (i j) ((1+ i) (1+ j))) space-3)
                        (reshape u* (τ (i j) ((1+ i) (1- j))) space-3)
  
positive.code:       ((~ start-1 2 end-1)
         (let ((space-1 (~ (1+ start-1) 2 end-1)))
           (fuse u*
                 (α #'* 0.5d0
                    (α #'+
                       (reshape u* (τ (i) ((1+ i))) space-1)
                       (reshape u* (τ (i) ((1- i))) space-1))))))
  
negative.code:              (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 #'* 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 #'* 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 #'* 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 #'* 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 #'* 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 #'* 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 #'* 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)
  