Specifying a Thematic Directory
We can affect a type to each node of the hierarchie
A type is a list of related names: transport, transport.plane
There is a subtyping constraint between categories and sub-categories
This constraint can be "implemented" using a thesaurus
makesense(Name, T)
|- List : T.Name
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|- category(cat_name Name, List) : T
"A category of name Name has type T if Name makes sense in T and if all subcategories have the type T.Name"
