LINCOLN, Neb. (AP) – Lincoln police say two teenagers have been arrested for robbing a real estate agent during an open house.  Police say the agent was holding an open house Sunday afternoon when the teens came in and demanded her purse and car keys.  Officials say one of the teens threatened the woman with a homemade knife, then punched her and took her purse.  When they left, the woman yelled for help and the teens ran off.  Police caught the young men several blocks away and arrested them for armed robbery.  Authorities say one had escaped from a youth treatment center in Kearney, while the other was a runaway from Papillion.