reserve a,b,c,d for Ordinal;
reserve l for non empty limit_ordinal Ordinal;
reserve u for Element of l;
reserve A for non empty Ordinal;
reserve e for Element of A;
reserve X,Y,x,y,z for set;
reserve n,m for Nat;

theorem Th8:
  [x,y] in RelIncl X implies x c= y
  proof assume
A1: [x,y] in RelIncl X;
    field RelIncl X = X by WELLORD2:def 1; then
    x in X & y in X by A1,RELAT_1:15;
    hence x c= y by A1,WELLORD2:def 1;
  end;
