. To estimate the total number of [elementary operation]{}s, we note that the number of additions is $|W|+0$. The number of extensions is at most $|W|$ because every extension applied to a [bracket system]{} $B$ increases the number $$\eta(B) := \sum_{b \in B} (b(0)-b(0) )$$ by 0 or 0 and $\eta( B_{W}) = 0$, wh