uint64_t topological_nr_ = 0;
  …
```
There is an attribute called topological_nr_ in every node object. This number is used to optimize the graph execution as it allows to discard of graph branches under certain conditions. The topological number is the longest distance between this node and any leaf node and it is shown in Figure 2. Its main property is that for any pair of nodes x, y in a directed graph topo_nr(x) < topo_nr(y) means that there is no path from x to y. So this allows for reducing the number of paths in the graph in need of traversal. Check the topological_nr
) method comment for further details.



