booc.io: An Education System with Hierarchical Concept Maps and Dynamic Non-linear Learning Plans. - Michail Schwab; Hendrik Strobelt; James Tompkin 001; Colin Fredericks; Connor Huff; Dana Higgins; Anton Strezhnev; Mayya Komisarchik; Gary King; Hanspeter Pfister (IEEE Trans. Vis. Comput. Graph., 2017)