Thousands of students at Mexico's National Autonomous University protest to demand an end to violence by groups of thugs known as "porros," who are often registered but don't attend classes, at the University's main campus in Mexico City, Wednesday, Sept. 5, 2018. Students at Mexico's largest university have gone on strike after a campus attack against protestors on Monday, in which two students were seriously injured. (AP Photo/Rebecca Blackwell), APTOPIX