Just about everything about the movie “Memento,” starring Guy Pearce and Carrie-Anne Moss, is a puzzle, including the Oscar category for which it was nominated. (Pay close attention here.) So, if it was screenwriter Jonathan Nolan’s published short story that inspired his co-screenwriter and director brother Christopher Nolan’s movie, why wasn’t “Memento” nominated for “Best Screenplay Based on Material Previously Published” instead of the category for which it received the nod, that of “Best Writing, Screenplay Written Directly for the Screen”? It’s a matter of semantics. The often-confusing film, about a determined man with short-term memory loss investigating his wife’s murder, actually premiered in France a mere week before Jonathan’s original short story was published in Esquire magazine .The movie was shot in a quick 25 days, primarily around Southern California’s low-rent Sunland-Tujunga area. Not that confusion is necessarily a bad thing. Already, the film has earned a Christopher Award and Best Screenplay prizes from the American Film Institute, the Boston Society of Film Critics, the Toronto Film Critics Association, the Broadcast Film Critics Association, the London Film Critics Circle, the Los Angeles Film Critics Association as well as the Waldo Salt Screenwriting Award from the Sundance Film Festival. Ah, but will it grab the Oscar gold? There’s the final puzzle.