description:
extract-category |x>
extract the category from the given ket
examples:
-- if there is no category, then return unchanged:
extract-category |fish>
|fish>
extract-category |animal: mammal: dog>
|animal: mammal>
extract-category |a: b: c: d: e: f>
|a: b: c: d: e>
see also:
extract-value