code: func (e *G2) Add(a, b *G2) *G2 {
  	if e.p == nil {
  		e.p = newTwistPoint(nil)
  	}
  	e.p.Add(a.p, b.p, new(bnPool))
  	return e
  }
docs: // Add sets e to a+b and then returns e.
  // BUG(agl): this function is not complete: a==b fails.