For example Birkhoff and Langer published an important extension in 1923. Birkhoff's work on linear differential equations, difference equations and the generalised Riemann problem mostly all arose from the basis he laid in his thesis.
Halimbawa Birkhoff at Langer-publish ng isang mahalagang extension in 1923. Birkhoff ng trabaho sa guhit kaugalian equation, pagkakaiba equation at ang generalised Riemann problema sa nakararami sa lahat ng arose mula sa mga batayan niya inihain sa kanyang sanaysay.