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Undercover officers will be looking for thugs and fare cheats on the 9 and 9X lines that run between downtown to Visitacion Valley.
The 14 line that travels through the Mission District to Daly City and the 49 line that cuts through the city from the Marina to Ingleside.
An 11-year-old student was stabbed in an unprovoked attack on that line this month.
Police say there has also been an alarming increase in robberies.
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