 reserve a,Z1,Z2,Z3 for set,
         x,y,z for object,
         k for Nat;
 reserve S for RelStr;
 reserve P,Q for non empty flat Poset;
 reserve p,p1,p2 for Element of P;
 reserve K for non empty Chain of P;
 reserve X,Y for non empty set;

theorem LemFlatten05:
  X is Element of FlatPoset(X)
  proof
    X in {X} by TARSKI:def 1;
    hence thesis by XBOOLE_0:def 3;
  end;
