reserve T for non empty Abelian
  add-associative right_zeroed right_complementable RLSStruct,
  X,Y,Z,B,C,B1,B2 for Subset of T,
  x,y,p for Point of T;

theorem
  (X` (O) B!)` = X (o) B
proof
  (X` (O) B!)` =(((X` (-) B!)` (-) B)`)` by Th37
    .=X (+) (B!)! (-) B by Th37
    .=X (+) B (-) B by Th1;
  hence thesis;
end;
