The relation至onR; The relation on Z, the relation c on P(A) partial order, (R, S),(Z, /), (P(A),S are partially ordered sets Example:LetA={1,2},P(A)={,{1},2},1,2}},the relation on the powerset ofA ={(,),(,{1}),(,{2}),(,{1,2}) (1},{1}),({1},{1,2})({2},{2})2({(2},{1,2}),({1,2},{1,2})}The relation ≦ on R； The relation | on Z+；the relation  on P(A)。 partial order， (R,≦), (Z+ ,/), (P(A),) are partially ordered sets。 Example： Let A={1,2},P(A)={,{1},{2},{1,2}}, the relation on the powerset of A: ={(,),(,{1}),(,{2}),(,{1,2}), ({1},{1}),({1},{1,2}),({2},{2}),({2},{1,2}),({1,2},{1,2})}