N=2 integer steps live below level 2

Every integer regional step with two elementary positions lives below level $2$.

The length equation already forces $lower < 3$, and level $2$ itself is impossible: at level $2$ the length equation gives $L=1$ while physical positions contain both halves of every parent occurrence. Hence only levels $0$ and $1$ carry content at $N=2$.

Formalization Note This combines the level bound $lower < 3$ with the level-two impossibility, both already proved nodes in the same environment.