f(x, y) := block([dx, dy],
	dx: divide(x + 2, 3),
	dy: divide(y + 2, 3),
	[dx[1] * 3 + dy[1] - 3, dx[2] * 3 + dy[2] + 1]
);

sudoku_pre1() := ([a,
	M: zeromatrix(9, 9)
	],
	for i: 1 thru 9 do (
		a: random(9) + 1,
		M[i][a]: 1
	),
	M
);

sudoku_pre2() := ([a, p,
	M: zeromatrix(9, 9),
	K: zeromatrix(9, 9)
	],
	for i: 1 thru 9 do (
		p: 0,
		for j: 1 while (p = 0) do (
			a: random(9) + 1,
			if K[i][a] = 0 then (
				p: 1,
				for k: i thru 9 do K[k][a]: 1,
				M[i][a]: 1
			)
		)
	),
	M
);

sudoku_pre3() := ([a, p, d,
	M: zeromatrix(9, 9),
	K: zeromatrix(9, 9)
	],
	for i: 1 thru 9 do (
		p: 0,
		for j: 1 while (p = 0) do (
			a: random(9) + 1,
			if K[i][a] = 0 then (
				p: 1,
				for k: 1 thru 9 do (
					d: f(f(i, a)[1], k),
					K[d[1]][d[2]]: 1
				),
				for k: i thru 9 do K[k][a]: 1,
				M[i][a]: 1
			)
		)
	),
	M
);

/*
sudoku_pre4() := ([a, p, d,
	M: zeromatrix(9, 9), 
	K: zeromatrix(9, 9)
	],
	for l: 1 thru 9 do (
		for i: 1 while(i <= 9) do (
			p: 0,
			for j: 1 while (p = 0) do (
				a: random(9) + 1,
				if K[i][a] = 0 then (
					p: 1,
					for k: 1 thru 9 do (
						d: f(f(i, a)[1], k),
						K[d[1]][d[2]]: 1
					),
					for k: i thru 9 do K[k][a]: 1,
					M[i][a]: l
				)
			)
		),
		K: copymatrix(M)
	),
	M
);
*/

sudoku_pre5() := ([a, p, d, q,
	M: zeromatrix(9, 9), 
	K: zeromatrix(9, 9)
	],
	for l: 1 thru 9 do (
		q: 0,
		for i: 1 while (i <= 9 and q = 0) do (
			p: 0,
			for j: 1 while (p = 0 and q = 0) do (
				a: random(9) + 1,
				if not member(0, K[i]) then (
					q: 1
				) else (
					if K[i][a] = 0 then (
						p: 1,
						for k: 1 thru 9 do (
							d: f(f(i, a)[1], k),
							K[d[1]][d[2]]: 1
						),
						for k: i thru 9 do K[k][a]: 1,
						M[i][a]: l
					)
				)
			)
		),
		K: copymatrix(M)
	),
	M
);

sudoku_pre6() := ([a, p, d, q: 0,
	M: zeromatrix(9, 9), 
	K: zeromatrix(9, 9)
	],
	for l: 1 while (l <= 9 and q = 0) do (
		q: 0,
		for i: 1 while (i <= 9 and q = 0) do (
			p: 0,
			for j: 1 while (p = 0 and q = 0) do (
				a: random(9) + 1,
				if not member(0, K[i]) then (
					q: 1
				) else (
					if K[i][a] = 0 then (
						p: 1,
						for k: 1 thru 9 do (
							d: f(f(i, a)[1], k),
							K[d[1]][d[2]]: 1
						),
						for k: i thru 9 do K[k][a]: 1,
						M[i][a]: l
					)
				)
			)
		),
		K: copymatrix(M)
	),
	M
);

sudoku() := ([a, p, d, q, n: 100,
	M: zeromatrix(9, 9), 
	K: zeromatrix(9, 9),
	T: zeromatrix(9, 9)],
	for l: 1 while (l <= 9 and n >= 0) do (
		n: n - 1,
		q: 0,
		for i: 1 while(i <= 9 and q = 0) do (
			p: 0,
			for j: 1 while (p = 0 and q = 0) do (
				a: random(9) + 1,
				if not member(0, K[i]) then (
					q: 1,
					l: l - 1,
					K: copymatrix(T),
					M: copymatrix(T)
				) else (
					if K[i][a] = 0 then (
						p: 1,
						for k: 1 thru 9 do (
							d: f(f(i, a)[1], k),
							K[d[1]][d[2]]: 1
						),
						for k: i thru 9 do K[k][a]: 1,
						M[i][a]: l
					)
				)
			)
		),
		K: copymatrix(M),
		T: copymatrix(M)
	),
	if n < 0 then n else M
);