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

theorem
  Fint(A,2) = A^i^i
proof
  thus Fint(A,2)=Fint(A,1+1) .=(Fint(A,1))^i by Def4
    .=A^i^i by Th20;
end;
