Exotic Tetraquark Mesons in Large-Nc Limit: an Unexpected Great Surprise. - Bruno, G.E.; Chiodini, G.; Creanza, D.M.; Colangelo, P.; Corianò, C.; De Fazio, F.; Nappi, E.; Lucha, Wolfgang; Melikhov, Dmitri; Sazdjian, Hagop (EPJ Web of Conferences, 2018)