Magic Squares with initial constraints 

From the "Saarbrücker Zeitung"
The objective is the same as in the last puzzle, but some values in these
4x4squares are preset and/or positions are (by bold floor) constrained to
hold just numbers between 1 and 8 (the lower half of the domain).

The Prime Magic Square 

From Dudeney, Amusements in Mathematics, Number 410.
Another type of initial constraint:
Place the numbers 1 to 25 in the square so that every column, row,
and the two diagonals add up 65, with only prime numbers on the shaded
"T"
(the available primes are: 2, 3, 5, 7, 11, 13, 17, 19, and 23).

The Knight's Tour 

The goal here is to find an assignment of integers 1 .. 64 to the
fields of a chessboard, such that a knight could make a tour over the whole
board, using his normal moves (two forward, one sideways in any direction) and
stepping on the field labeled n in the nth move.
