readme: https://www.geogebra.org/m/cwcveget
  https://www.geogebra.org/m/b8dzxk6z
  https://www.geogebra.org/m/nqanttum
  https://www.geogebra.org/m/pd3g8a4u
  https://www.geogebra.org/m/jw8324jz
  https://www.geogebra.org/m/wjbpvz5q
  https://www.geogebra.org/m/qm3g3ma6
  https://www.geogebra.org/m/sdajgph8
  https://www.geogebra.org/m/e3ghhcbf
  https://www.geogebra.org/m/msne4bfm
  https://www.geogebra.org/m/nmcv2te5
  https://www.geogebra.org/m/hguqx6cn
  https://www.geogebra.org/m/jnyvpgqu
  https://www.geogebra.org/m/syctd97g
  https://www.geogebra.org/m/nq9erdby
  https://www.geogebra.org/m/au4har8c