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+p) (o) Y = (X (o) Y)+p
proof
  thus (X+p) (o) Y = ((X (+) Y)+p) (-) Y by Th15
    .= (X (o) Y)+p by Th14;
end;
