surface -- the surface key of a Divisor or a Curve

i1 : C = curve(5,2);

i2 : D = divisor C

o2 = {4, 2, 1, 1, 1, 1, 1}

o2 : Divisor

i3 : Q = surface D

                             2            2        2          2                        2            2         2          2         3
o3 = ideal(2495x x x  + 4036x x  - 5934x x  - 2495x x  - 4289x x  - 1194x x x  + 10682x x  - 8366x x  + 214x x  + 4197x x  - 11134x )
                0 1 2        1 2        1 2        0 3        1 3        1 2 3         2 3        0 3       1 3        2 3         3

o3 : CubicSurface