“…The C-lower approximations and the C-upper approximations of S and S c , obtained by means of multigraded dominance relations, are: (1,4), (1,5), (1,6), (1,8), (3,2), (3,4), (3,5), (3,6), (3,8), (7,2), (7,4), (7,5), (7,6), (7,8) C(S c ) = (2,1), (2,7), (4,1), (4,3), (4,7), (5,1), (5,3), (5,7), (6,1), (6,3), (6,7), (8,1), (8,7) All the remaining 36 pairs of reference objects belong to the C-boundaries of S and S c , i.e. Bn C (S) = Bn C (S c ).…”