13.1 Nullability in the valuator

In the valuator, every nulling tree is pruned back to its topmost nulling symbol. This means that there are no nulling rules in the valuator, only nulling symbols. For an example of how this works, see Example of nulled symbol.

While this may sound draconian, the “lost” semantics of the nulled rules and non-topmost nulled symbols are almost never missed. Nulled subtrees cannot contain input, and therefore do not contain token symbols. So no token values are lost when nulled subtrees are pruned, and we are dealing with the semantics of the empty string. See Evaluating nulled symbols.