Complex sentence: It is essentially a two-dimensional version of Nim--though non-trivial, the first player can always win, at least in the 5 by 5 matrix version by choosing the center piece and symmetrically mirroring the second player's moves.
Split into simpler sentences: It is essentially a two-dimensional version of Nim. Though non-trivial, the first player can always win, at least in the 5 by 5 matrix version by choosing the center piece and symmetrically mirroring the second player's moves.