I use the word "function" with both meanings:[br][list][*]real and complex functions with mathematical meaning, in Japanese, I use "函数 (Hánshù)".[/*][*]command function with computational meaning, in Japanese, I use "関数 (Guān shù)".[br][/*][/list][br]GeoGebra is a Dynamic Geometry Software (DGS).[br][list][*]DGS is a computer program which allows one to create geometric constructions with emulated compass and ruler.[/*][*]What is the merit of computer program? accuracy, reproducibility, repeatability, interactivity, encapsulability, ...[/*][/list][br]In the sense of numerical computing, there are some errors on floating point arithmetics.[br]When you use a computer algebra system, we can expect exact calculus. [br]But, in drawing, in many cases, we don't need accuracy?[br]