 reserve a,Z1,Z2,Z3 for set,
         x,y,z for object,
         k for Nat;

theorem
  for P,Q being chain-complete non empty Poset,
      L being non empty Chain of [:P,Q:] holds
    sup L = [sup (proj1 L), sup (proj2 L)] by YELLOW_3:46,LemProdPoset06;
