Since adjacent descendents in the general tree become successive right descent elements in the binary tree, we may consider m1 as the smaller, and m2 as the larger, of two adjacent descendents of a parental n in the general tree.
Every descendent is derived from an odd parent, call it m .
If n is the immediate left descendent of an odd m , then n is not an extension. Let n be the immediate left descendent of odd m . Then m is congruent to 1 or 2 mod 3, since odd numbers congruent to 0 mod 3 are leaves. The parent m may be an extension depending on whether j is congruent to 2 mod 4. Then n is not an extension.