Most trilogies are works of fiction involving the same characters or setting, such as "The Deptford Trilogy" of novels by Robertson Davies and "The Apu Trilogy" of films by Satyajit Ray. Other fiction trilogies are connected only by theme: for example, each film of Krzysztof Kieślowski's "Three Colors" trilogy explores one of the political ideals of the French Republic (liberty, equality, fraternity). Trilogies can also be connected in less obvious ways, such as "The Nova Trilogy" of novels by William S. Burroughs, each written using cut-up technique.