def partially_valid_public_key?(point)
      return false if point.group != self
      return false if point.infinity?
      point_satisfies_equation?(point)
    end
def partially_valid_public_key?(point)
      return false if point.group != self
      return false if point.infinity?
      point_satisfies_equation?(point)
    end
Returns true if the point is not infinity and it is a solution to
 the curve's defining equation.  This is defined in
 SEC1 2.0, Section 3.2.3.1: Elliptic Curve Public Key Partial Validation Primitive