On November 14, the reference to the Tables in the problem statement has
been updated. Before it contained a missing reference.



> Can you give me an example of which
  are the neighbors of e.g. the top left corner?


For a board 3x3:

123
456
789

the top left corner (1) has neighbours 254 (the trivial ones) plus
78 (wrapping the top border with the lower border) plus
36 (wrapping the left border with the right border)
9 (wrapping all borders).

An example with a 16x16 board is available from the checker. In the
checker it is also shown how to calculated the cell indices. You can
reuse that code.



> Is there a gecode costraint for the bitwise xor of two integer
> variables? I can't seem to find something like that.


try to look at Figure 4.2 on page 61 of the manual of gecode 5.0.0.


> do we get template .cpp file in which we write our model, similar to
> the one from the first assignment. Or do we have to make that for
> ourselves?


no, I will not provide a template this time because there are no
external data to read. Therefore, yes, you should start developing by
yourself. You can start either from the script of Assignment 1 (in this
case you will not need to include the files csvgetlinec++.* and Input.*)
or from one of the examples that come with Gecode. The Makefile can be
kept the same as in Assignment 1 or the previous exercise on the
Send-More-Money.