*L*, ⊑) (our problem has a lattice that is also distributive, so you may presume that) and a node

*x*in that lattice,

efficientlycompute the set

*S*⊆

*L*= {

*y*∈

*L*:

*x*⊏

*y*∧ ∄

*z x*⊏

*z*⊏

*y*}. This is well defined, and starting from ⊥ it is possible to walk the entire lattice easily (which is why we care). If you precompute the lattice you can do this trivially. Is it possible to do so without considering every node in the lattice?

Failing that, can you give me an efficient algorithm for computing the structure of the lattice from a set *L* and a partial order ⊑ ?