Carvalho Gastaldo, Brunno, et al. “Five Years of PCK Summit, What Has Endured: 1. A Descending Hierarchical Classification of the Science PCK Published Papers”. Enseñanza De Las Ciencias: Revista De investigación Y Experiencias didácticas, no. Extra, Feb. 2018, pp. 595-00, https://raco.cat/index.php/Ensenanza/article/view/334692.