So the article first states a mathematical definition: > A bounded lattice is a mathematical structure that has a least element (bot), a greatest element (top)

So the article first states a mathematical definition: > A bounded lattice is a mathematical structure that has a least element (bot), a greatest element (top) And then proceeds to define a typeclass that does not satisfy the definition: instance (Ord k, Lattice a) => Lattice (Map k a) where top = error $ "Cannot be represented. :-( You can't even fix the definition of top, since union of arbitrary Maps is not bounded, e.g. there is no finite Map String foo (map with String keys) that is a superset of every Map String foo. You could change Lattice to a weaker structure, but I think it would be better to present a simpler typeclass like Show or Ord.