Collections can be both free* and compelling: https://www-cs-faculty.stanford.edu/~knuth/diamondsigns/diam.html https://www-cs-faculty.stanford.edu/~knuth/diamo

Collections can be both free* and compelling: https://www-cs-faculty.stanford.edu/~knuth/diamondsigns/diam.html https://www-cs-faculty.stanford.edu/~knuth/diamondsigns/diam... * at least in capital cost. I imagine he expended plenty of time and travel on the subject.