In killer sudoku(sum number place) we get rid of the clues and replace them with sums and cages...
Now the "mother" of killer sudoku, Ms Miyuki Misawa, has gone one step further - she got rid of the sums and replaced them with < and = !
Original page
Her homepage
Just 8 symbols in the 2nd one... but it does yield a unique solution! How beautiful!
[Edit: picture taken off.]