A Jewish man looks on at a pro-Palestinian encampment at Columbia University in New York. Photograph: Leonardo Munoz/AFP via Getty Images The easiest way to reach Columbia University is to exit the red line train at 110th and Broadway, walk past Tom’s Diner, the beloved corner cafe decorated with Seinfeld memorabilia in honour of the television show that made it famous, and stroll up to the front gates. Springtime is usually beautiful on the campus, and the gates are usually open to visitors. Late April means exam time and residents are accustomed to hearing blood-curdling howls on the last Sunday...