favico from: https://commons.wikimedia.org/wiki/File:GeoGebra_button_show_checkbox.gif https://github.com/DanWahlin/AngularIn20TypeScript https://github.com/jelbourn/material2-app https://www.youtube.com/watch?v=rRiV_b3WsoY https://www.youtube.com/watch?v=WAPQF_GA7Qg https://www.youtube.com/watch?v=7cBaE_QwFWQ https://www.youtube.com/watch?v=mnkG-RRkZtU https://www.youtube.com/watch?v=53bdrz7cZ-c