reserve k,m,n for Nat,
  i1,i2,i3 for Integer,
  e for set;
reserve i,k,m,n,p,x,y for Nat;

theorem Th11:
  k-SD c= INT
proof
  let e be object;
  assume e in k-SD;
  then e is Integer by Th10;
  hence thesis by INT_1:def 2;
end;
