Equations for the Fibre 13

    We formulate   f-1(FQ)   as a system of homogeneous equations.
Our coordinates are symmetric 4x4-matrices

l1 := x-axis with coordinates [w,x,0,0]
l2 := y-z line at infinity with coordinates [0,0,y,z]

General (2,2)-form     Fgen   :=   C22x2z2 + C21x2yz + ... + C00w2y2

FQ   =     (el-g2)x2z2   +  2(bl-dg)wxz2   +  (al-d2)w2z2 +  2(ek-gf)x2yz   +  2(2bk-cg-df)wxyz
          +  2(ak-dc)w2yz +  (eh-f2)x2y2   +  2(bh-cf)wxy2   +  (ah-c2)w2y2 .
Equations for the fibre:   Fgen   =   FQ .