(
  (GIVEN w x y z)

    ; IM1 := 
    ; [ 20  -84  -12  -20 ]
    ; [                   ]
    ; [  0   16  -12   0  ]
    ; [                   ]
    ; [  0   12   16   0  ]
    ; [                   ]
    ; [  0   0    0    5  ]

    (= w1 (* +20 w))
    (= x1 (+ (+ (* -84 w) (* +16 x)) (* 12 y)))
    (= y1 (+ (+ (* -12 w) (* -12 x)) (* 16 y)))
    (= z1 (+ (* -20 w) (* +5 z)))
  
    (= ax1 (- (ABS x1) w1))
    (= ay1 (- (ABS y1) w1))
    (= az1 (- (ABS z1) w1))
    
    (= c1 (max (max ax1 ay1) az1))

    ; IM2 := 
    ; [ 25  -51  -93  -25 ]
    ; [                   ]
    ; [  0   7   -24   0  ]
    ; [                   ]
    ; [  0   24   7    0  ]
    ; [                   ]
    ; [  0   0    0    5  ]

    (= w2 (* +25 w))
    (= x2 (+ (+ (* -51 w) (* +7 x)) (* +24 y)))
    (= y2 (+ (+ (* -93 w) (* -24 x)) (* +7 y)))
    (= z2 (+ (* -25 w) (* +5 z)))
  
    (= ax2 (- (ABS x2) w2))
    (= ay2 (- (ABS y2) w2))
    (= az2 (- (ABS z2) w2))
    
    (= c2 (max (max ax2 ay2) az2))

    ; IM3 := 
    ; [ 10   6  42  -10 ]
    ; [                 ]
    ; [  0   8   6   0  ]
    ; [                 ]
    ; [  0  -6   8   0  ]
    ; [                 ]
    ; [  0   0   0   5  ]

    (= w3 (* +10 w))
    (= x3 (+ (+ (* +6 w) (* +8 x)) (* -6 y)))
    (= y3 (+ (+ (* +42 w) (* +6 x)) (* +8 y)))
    (= z3 (+ (* -10 w) (* +5 z)))

    (= ax3 (- (ABS x3) w3))
    (= ay3 (- (ABS y3) w3))
    (= az3 (- (ABS z3) w3))
    
    (= c3 (max (max ax3 ay3) az3))
  
    ; IM4 := 
    ; [ 3  -9  9  -3 ]
    ; [              ]
    ; [ 0   3  0   0 ]
    ; [              ]
    ; [ 0   0  3   0 ]
    ; [              ]
    ; [ 0   0  0   1 ]

    (= w4 (* +3 w))
    (= x4 (+ (* -9 w) (* 3 x)))
    (= y4 (+ (* +9 w) (* 3 y)))
    (= z4 (+ (* -3 w) z))
    
    (= ax4 (- (ABS x4) w4))
    (= ay4 (- (ABS y4) w4))
    (= az4 (- (ABS z4) w4))
    
    (= c4 (max (max ax4 ay4) az4))
    
    (= floor z)
    
    (= wall (- (* 6 w) y))
    
    (= bg (min floor wall))
  
  (RETURN (min (min (min c1 c2) (min c3 c4)) bg))
  ; (RETURN (min c2 bg))
  ; (RETURN bg)
  ; (RETURN (min (min c1 c2) bg))
)