SANTA CRUZ — The first slide professor Nirvikar Singh flashed on his PowerPoint showed the faces of six Sikh worshipers gunned down the previous month in Oak Creek, Wis., by a man with white supremacist ties.

As after other attacks since 9/11, the UC Santa Cruz professor explained to students in this fall introductory course, the Wisconsin shooting revealed an abiding ignorance over who Sikhs are -- and aren't.