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

theorem
  for n being Nat holds Fcl(A,n) \/ Fcl(B,n) = Fint((A \/ B)` ,n)`
proof
  let n be Nat;
  Fcl(A,n) \/ Fcl(B,n) = Fcl(A \/ B,n) by Th17
    .= Fint((A \/ B)`,n)` by Th27;
  hence thesis;
end;
