https://sv.wikipedia.org/wiki/Roman_Opa%C5%82ka
https://culturainquieta.com/es/arte/ilustracion/item/15516-roman-opalka-invirtio-la-mitad-de-su-vida-dibujando-numeros-del-1-hasta-el-infinito.html
http://www.artnet.com/artists/roman-opalka/
https://designyoutrust.com/2019/05/roman-opalka-the-polish-artist-who-spent-half-his-life-painting-from-1-to-infinity/