Erdély, Daniel (2004). "Concept of the Spidron System"(PDF). Archived from the original(PDF) on 2011-12-15. Retrieved 2011-12-28. In: Proceedings of Sprout-Selecting Conference: Computer Algebra Systems and Dynamic Geometry Systems in Mathematics Teaching. C. Sárvári, ed. University of Pécs, Pécs, Hungary.
Erdély, Daniel (2004). "Concept of the Spidron System"(PDF). Archived from the original(PDF) on 2011-12-15. Retrieved 2011-12-28. In: Proceedings of Sprout-Selecting Conference: Computer Algebra Systems and Dynamic Geometry Systems in Mathematics Teaching. C. Sárvári, ed. University of Pécs, Pécs, Hungary.