paragraph_text: <!--- POTREBAN PRIJEVOD Gell-Mann's work in the 1950s involved the understanding of a class of then newly discovered elementary particles which came to be called kaons and hyperons. Classifying these particles led to the idea of a new quantum number called strangeness. One of Gell-Mann's triumphs is the Gell-Mann–Nishijima formula, which was, initially, a formula from empirical results, but was later explained by the quark model. Gell-Mann and Abraham Pais were involved in explaining many puzzling aspects of the physics of these particles.