Perhaps the most important feature of Kästner's contributions was his interest in the parallel postulate which indirectly influenced Bolyai and Lobachevsky too. Kästner taught Bolyai 's father and J M C Bartels, one of Kästner's students, taught Lobachevsky . Folta writes in about Kästner's work on geometry:
Marahil ang pinaka-mahalagang katangian ng Kästner ang kontribusyon ay ang kanyang interes sa pagpaparis-kuro na hindi tuwiran naiimpluwensyahan Bolyai at Lobachevsky masyadong. Kästner tinuturuan Bolyai 's ama at JMC Bartels, isa sa Kästner ng mga mag-aaral, tinuturuan Lobachevsky. Folta magsusulat sa tungkol sa Kästner ng trabaho sa geometry: