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Class HistoryCrum
invariant: the parent's trace >= the child's trace
The subclasses should differentiate between the number
of children: 0, 1, or more. ORoots have 0 children and
always have a canopyCrum. HCrums for OCrums in the
body of the ent have one child if they are at the top
of an unshared subtreee, and more if they are at the top
of a shared subtree. HCrums with more than one child
almost always have a canopyCrum to represent the join
between the canopies of their multiple hchildren.
The change would make the updateH method return a
new crum, which the oCrums would install.
They don't do so now because I'm not sure if a crum with
no parents can appear in the middle of the ent. If so, then
the version compare operations would gag. Hmmm. The
change doesn't make any difference for that....
Package: Udanax-Gold
All Superclasses: Object Heaper
Immediate Subclasses: HBottomCrum HUpperCrum
Protocols: Object
Categories: Xanadu-Be-Ents