The last time we looked it was a work in progress. That was a year ago. William Osborne and Abbie Conant had been working on it for so long, Osborne said at the time, that it felt like “forever.” But now their music theater chamber piece is about to get its world premiere. The name of the piece, “Aletheia,” comes from the ancient Greeks, who “had several words for truth,” he pointed out. “‘Aletheia’ is one and means creating a space where truth can appear.” Conant is to perform the work on Friday in Southern California at the University of Redlands, which is hosting it as part of the 46th International Trombone Festival.