[trace]  ?- flatten(S, FlatS), init(e, S).
   Call: (8) init(e, _G312) ? creep
   Exit: (8) init(e, [[1, 2, 3], [4, 5, 6], [7, 8, 0]]) ? creep

S = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
FlatS = [[[1, 2, 3], [4, 5, 6], [7, 8, 0]]] 

Yes
[debug]  ?- init(e, S), flatten(S, FlatS).

S = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
FlatS = [1, 2, 3, 4, 5, 6, 7, 8, 0] 

Yes
[debug]  ?- init(e, S), flatten(S, FlatS).

S = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
FlatS = [1, 2, 3, 4, 5, 6, 7, 8, 0] 

Yes
[debug]  ?-