/* this=this^p using Frobenius */
public void Frob(FP2 f)
{
FP2 f2 = new FP2(f);
FP2 f3 = new FP2(f);
f2.Sqr();
f3.Mul(f2);
a.Frob(f3);
b.Frob(f3);
c.Frob(f3);
b.PMul(f);
c.PMul(f2);
}