Axiom HleafNodeConst: forall x p leafIdx lvl dt,
              isLeafNode x (writeToNode p leafIdx lvl dt) ->
              isLeafNode x p.

Lemma zero_sum: forall s memSz leafIdx lvl dt, match s with |(s', (l, p)) => init_invariant s memSz -> init_invariant (s', (popStash l dt, writeToNode p leafIdx lvl dt ) ) memSz end.