From left to right: Veronica, Dulce and Katia attend a Mayan mathematics class at Ignacio Ramirez Calzada primary school in indigenous Celtun community in Chichimila, Yucatan, Mexico on December 18, 2017. Maya mathematics constituted the most sophisticated mathematical system ever developed in the Americas. The Maya counting system required only three symbols to form all their numbers: a dot representing one, a bar representing five, and a shell representing 20 or zero, depending on its placement. The Maya used a base 20 (vigesimal) numerical system, unlike our current base 10. (Photo by Bénédicte Desrus)