The Challenger puzzle can be found syndicated in various
newspapers (The Toronto Star for example).
It involves filling in the entries of a 4 by 4 grid with
integers between 1 and 9 so that all columns rows and diagonals add up
to numbers given in the puzzle. Some of the numebrs are already filled
in the grid so these act as a constraint on the other solutions. Write
a procedure which will solve any Challenger puzzle. Remember
that the solutions can only be integers between 1 and 9.