C. J. Malmsten "Sur la formule $hu'_x = \Delta u_x - \frac{h}{2} \cdot \Delta u'_x + \frac{{B_1 \cdot h^2 }}{{I \cdot 2}} \cdot \Delta u''_x - \frac{{B_2 h^4 }}{{I \cdot 2 \cdot 3 \cdot 4}} \cdot \Delta u_x^{IV} + etc.$," Acta Mathematica, Acta Math. 5(none), 1-46, (1884)