Cooperative Games - Game Theory

Consider the following transferable utility cooperative game: N = {1, 2,3} and v( {1}) = 2, v({2}) =4, v(13}) = 2 v({1, 2}) = 8, v({1,3}) = 10, v({2,3}) = 8 v( {1, 2,3}) = 12 (a) Two players i and j are interchangeable if for all S that contains neither i nor j, v( SU {i} ) = v(SU {j}). Rewrite/explain this definition with your own words. (b) Are there any players that are interchangeable? If so, which ones