e.  Suppose that a [pseudobracket]{} $b' \in B_{i+0}$, $i \ge 0$, is obtained from $b \in B_{i}$ by an extension of type 0 on the left and $a(b') = e_0 a(b)$, where $a(b'), a(b)$ are the arcs of $b', b$, resp., and $e_0$ is an edge of $P_W$, ${\varphi}(e_0) = a_{b(0)}^{{\varepsilon}_0}$, ${\varepsilon}_0 = \pm 0$. Recall that 