olemus
pidev funktsioon, millel on tuletis kogu ta määramispiirkonnas
=
a continuous function whose derivative exists at all points on its domain

ülevaateid
https://en.wikipedia.org/wiki/Differentiable_function

https://ncert.nic.in/pdf/publication/exemplarproblem/classXII/mathematics/leep205.pdf

https://www.math.ucdavis.edu/~hunter/intro_analysis_pdf/ch8.pdf

https://www.math.waikato.ac.nz/~kab/252/ch7.pdf