code: def RobustCrossProd(self, other):
      
      assert(self.IsUnitLength() and other.IsUnitLength())
      x = self.Plus(other).CrossProd(other.Minus(self))
      if abs(x.x) > 1e-15 or abs(x.y) > 1e-15 or abs(x.z) > 1e-15:
        return x.Normalize()
      else:
        return self.Ortho()
docs: A robust version of cross product.  If self and other
      are not nearly the same point, returns the same value
      as CrossProd() modulo normalization.  Otherwise returns
      an arbitrary unit point orthogonal to self.