static Item* right_column (Grob *me);
static Item* left_column (Grob *me);
static Drul_array<Skyline> skylines (Grob *me, Grob *right_col);
static Item* right_column (Grob *me);
static Item* left_column (Grob *me);
static Drul_array<Skyline> skylines (Grob *me, Grob *right_col);