Now I wonder if there are any 5x5 nonograms which can be proven to require multiple levels of backtracking, i.e. where you have to make at least two guesses before reaching a contradiction, no matter where you put those guesses.
1 1 1
1 1 1 2 1
2 . . . . .
2 . . . . .
11 . . . . .
11 . . . . .
1 . . . . . 1 1 1
1 1 1 2 1
2 x x . . .
2 . . x x .
11 x . . x .
11 . x . . x
1 . . x . .
1 1 1
1 1 1 2 1
2 x x . . .
2 . . x x .
11 . x . x .
11 x . . . x
1 . . x . .