Everyone knows that Friday crosswords are the most arduous of the week, created for the finely tuned brains of experienced solvers. Those puzzle mavens can rev up their gray matter on these super-strenuous grids. Only about two-thirds of the 72 crosswords have themes—“Chapter and Verse,†“Radical Chic,†“Dress Codeâ€â€”and there's always something tremendously tricky going on, too.