$ http://en.wikipedia.org/wiki/Survo_Puzzle, under "Swapping method"
$ (open puzzle)
ESSENCE' 1.0
param r be 4;
param c be 4;
param rowsums be [51,36,32,17];
param colsums be [51,42,26,17];
param game be
   [
     [0, 0, 0, 0],
     [0, 0, 0, 0],
     [0, 0, 0, 0],
     [0, 0, 0, 0]
   ]