State and federal policemen clash with teachers from Section 22 of the National Union of Education Workers during the visit of Mexican President Felipe Calderon in Oaxaca, Mexico, on Feb. 15, 2011. Teachers tried to prevent the arrival of President Felipe Calderon to the Government Palace in Oaxaca and clashed with policemen, leaving at least 13 injured, including policemen, teachers and members of the press, according to the authorities. [Xinhua/Maximiliano Nunez]