(4,8):(1,4)
    0   4   8  12  16  20  24  28
    1   5   9  13  17  21  25  29
    2   6  10  14  18  22  26  30
    3   7  11  15  19  23  27  31
(4,8):(8,1)
    0   1   2   3   4   5   6   7
    8   9  10  11  12  13  14  15
   16  17  18  19  20  21  22  23
   24  25  26  27  28  29  30  31
(4,(2,4)):(2,(1,8))
    0   1   8   9  16  17  24  25
    2   3  10  11  18  19  26  27
    4   5  12  13  20  21  28  29
    6   7  14  15  22  23  30  31
h((1,5)) = 19  h((1,(1,2))) = 19  h(5) = 3
一维坐标 0..7 → [0, 2, 4, 6, 1, 3, 5, 7]
size = 32  cosize = 32  rank = 2  h[1] = (2,4):(1,8)
coalesce((2,(1,6)):(1,(6,2))) = 12:1
coalesce((4,8):(1,4)) = 32:1  coalesce((4,8):(8,1)) = (4,8):(8,1)
