Function: ellbil
Section: elliptic_curves
C-Name: bilhell
Prototype: GGGp
Help: ellbil(E,z1,z2): canonical bilinear form for the points z1,z2 on the
 elliptic curve E. Either z1 or z2 can also be a vector/matrix of points.
Doc:
 if $z1$ and $z2$ are points on the elliptic
 curve $E$ this function
 computes the value of the canonical bilinear form on $z1$, $z2$:
 $$ ( h(E,z1\kbd{+}z2) - h(E,z1) - h(E,z2) ) / 2 $$
 where \kbd{+} denotes of course addition on $E$. In addition, $z1$ or $z2$
 (but not both) can be vectors or matrices.