Problem
Consider a BLP system with the following clearances (classifications) and category sets: 3 clearances/classifications: U ≤ S ≤ TS
3 category sets: {ASIA,EUR,US}, {EUR,US}, {US} (Notice: don't consider other unlisted category sets, like {ASIA} or {EUR}. They won't appear in the system)
List all the security levels in the system.
By Denning's axioms, those security levels form a lattice.
Draw the lattice in full detail (with all the security levels you have listed above; don't write something like lattice1×lattice2).
Assuming Alice is assigned the security level (U, {ASIA,EUR,US}), list all the security levels (of objects) that she can read and all the security levels (of objects) that she can write by BLP policy.