Extensions and Left Descent Elements are Disjoint Sets

-- easily proven (thanks to Margaret Maxfield)

-- supports the dissection of the binary tree into left descent assemblies (l.d.a.s)

       -- The l.d.a. headers (in {5[8])} are collected as the root of abstract predecessor tree.

       -- No left descent elements are in {5[8]}, only {(1,3, and 7)[8]}.

       -- All l.d.a.s are completed by a leaf node set (in {0[3]}) in the abstract predecessor tree.

-- Thus all elements of the binary predecessor tree appear in the abstract predecessor tree.