reserve T for non empty RelStr,
  A,B for Subset of T,
  x,x2,y,z for Element of T;

theorem Th15:
  Fcl(A,1) = A^b
proof
  (Fcl A).0=A by Def2;
  then (Fcl A).(0+1)=A^b by Def2;
  hence thesis;
end;
