+Real
+Paper_column::minimum_distance (Grob *left, Grob *right)
+{
+ Drul_array<Grob*> cols (left, right);
+ Drul_array<Skyline> skys = Drul_array<Skyline> (Skyline (RIGHT), Skyline (LEFT));
+
+ Direction d = LEFT;
+ do
+ {
+ Skyline_pair *sp = Skyline_pair::unsmob (cols[d]->get_property ("horizontal-skylines"));
+ if (sp)
+ skys[d] = (*sp)[-d];
+ }
+ while (flip (&d) != LEFT);
+
+ return max (0.0, skys[LEFT].distance (skys[RIGHT]));
+}
+