cantor attended lectures weierstrass ref name mactutor published examples subsets real line known cantor sets unusual properties recognized fractals ref name classics also last part century felix klein henri poincar introduced category fractal come called self inverse fractals ref name mandelbrot julia set fractal related mandelbrot set alt x px sierpinski gasket generated fractal tree x px one next milestones came helge von koch extending ideas poincar dissatisfied weierstrass 's
Formal science Mathematics Applied mathematics Dynamical systems Fractal geometry