exceptionalDivisor -- get the exceptional divisor of a blowup

i1 : T = abstractProjectiveSpace 2

o1 = T

o1 : a flag bundle with subquotient ranks {1..2}

i2 : S = abstractProjectiveSpace 0

o2 = S

o2 : a flag bundle with subquotient ranks {1, 0}

i3 : i = map(T,S,OO_S) -- inclusion of a point in P^2

o3 = i

o3 : a map to T from S

i4 : X = first blowup(i)

o4 = X

o4 : an abstract variety of dimension 2

i5 : exceptionalDivisor X

o5 = a sheaf

o5 : an abstract sheaf of rank 1 on X

i6 : chern oo

o6 = 1 + E
          0

               QQ[][h, H   ..H   ]
                        2,1   2,2
     --------------------------------------[E ]
     (- h - H   , - h*H    - H   , -h*H   )  0
             2,1       2,1    2,2      2,2
o6 : ------------------------------------------
                           2
                 (H   E , E  + H   )
                   2,1 0   0    2,2