UNIVERSITY OF VIRGINIA LAW — Douglas Laycock doesn’t remember all the events surrounding his public high school’s 1963 Christmas assembly. Half a century of appellate litigation, writing and teaching will do that. But he does clearly remember hearing the Christian Nativity story from the Gospel of Luke. And he remembers walking out in protest. Laycock, who retires from the University of Virginia School of Law in May as perhaps the nation’s preeminent expert on religious liberty — and one of its most effective advocates — said an outspoken atheist he was sitting next to helped him take the plunge.