nitc :: POSetGroupColorer :: buckets
For each holder, the collection of introduced elements is given.
A single element must not be introduced in more than one holder.
# The elements to color.
#
# For each holder, the collection of introduced elements is given.
#
# A single element must not be introduced in more than one holder.
var buckets: Map[H, Collection[E]]
src/compiler/coloring.nit:298,2--303,35