code: func (e *gfP6) MulTau(a *gfP6, pool *bnPool) {
  	tz := newGFp2(pool)
  	tz.MulXi(a.x, pool)
  	ty := newGFp2(pool)
  	ty.Set(a.y)
  	e.y.Set(a.z)
  	e.x.Set(ty)
  	e.z.Set(tz)
  	tz.Put(pool)
  	ty.Put(pool)
  }
docs: // MulTau computes τ·(aτ²+bτ+c) = bτ²+cτ+aξ