Comment #67 on issue 2801 by [email protected]: Patch: Approximates
cross-staff slurs in VerticalAxisGroup vertical-skylines.
http://code.google.com/p/lilypond/issues/detail?id=2801
In outside-staff-spacing, for example, if grobs can slide other under
grobs, they do, which means that they are no longer part of the sideline.
It is not a linear distinction:
if (stashable_under_other_grob)
stash;
else
place_over
The skyline changes from having the extent of the grob to not in a
non-gradual way.
This sorta thing can be articulated through mixed integer linear
programming using 1 for true and 0 for false, but it would become
mixed-integer quadratic because you're multiplying these 1s and 0s by other
things that are themselves variables in the linear program. I know of no
package that supports this sorta thing and it seems like it'd take for ages
even if it were possible
