1. Crack sells for as little as $2 a hit in thousands of so–called tienditas, or little drug shops, that have sprung up in cities since drug abuse emerged as a serious problem in Mexico in the 1''0s. Crack is the No. 1 problem we have in our cities,‘‘ said Victor Guisa, head of the government‘s '6 drug rehabilitation clinics. Addicts end up smoking vast quantities of rocks, making them strung out and prone to violence and schizophrenia.‘‘ Gang violence surrounding Mexican drug consumption now mixes with bloodshed unleashed by the big smuggling cartels, adding up to more than 1,500 drug–related killings last year. All these crimes we are seeing, all these executions have more to do with street dealing than with the big narcotics trafficking,‘‘ said Attorney General Daniel Cabeza de Vaca.