'BEGIN'
	'COMMENT'
		FIND A SOLUTION FOR THE `N QUEEN' PROBLEM.
		(GOT THE ALGORITHM FROM A MODULA PROGRAM FROM
		 MARTIN NEITZEL).
	;

	'INTEGER' N, MAXN;

	MAXN := 9;		'COMMENT' MAXIMUM SIZE;
	N := 2;			'COMMENT' CURRENT SIZE;

TRY NEXT N:

	'BEGIN'

	'INTEGER' 'ARRAY' COLUMN [1 : N];
	'BOOLEAN' 'ARRAY' EMPCOL [1 : N];
	'BOOLEAN' 'ARRAY' EMPUP [-N+1 : N-1];
	'BOOLEAN' 'ARRAY' EMPDO [2 : 2*N];
	'INTEGER' I;

	'PROCEDURE' PRINT;
	'COMMENT'
		PRINT THE CURRENT SOLUTION IN A CHESSBOARD ALIKE
		PICTURE ;
	'BEGIN'
		'INTEGER' I, J;

		'PROCEDURE' OUTFRAME;
		'BEGIN'
			'INTEGER' I;

			'FOR' I := 1 'STEP' 1 'UNTIL' N 'DO'
				OUTSTRING (1, `+---');
			OUTSTRING (1, `+\N')
		'END';

		OUTSTRING (1, `SEE:\N') ;

		'FOR' J := 1 'STEP' 1 'UNTIL' N 'DO' 'BEGIN'
			OUTFRAME;
			OUTSTRING (1, `|');
			'FOR' I := 1 'STEP' 1 'UNTIL' N 'DO' 'BEGIN'
				'IF' N + 1 - J = COLUMN [I] 'THEN'
					OUTSTRING (1, ` Q |')
				'ELSE'
					OUTSTRING (1, `   |')
			'END';
			OUTSTRING (1, `\N')
		'END';
		OUTFRAME
	'END';


	'PROCEDURE' SET (X);
	'VALUE' X;
	'INTEGER' X;
	'BEGIN'
		'INTEGER' Y;
	
		'FOR' Y := 1 'STEP' 1 'UNTIL' N 'DO'
		'BEGIN'
	    		'IF' EMPCOL [ Y ] 'AND' EMPUP [ X-Y ] 
					'AND' EMPDO [ X+Y ] 'THEN'
			'BEGIN'
				COLUMN [ Y ] := X ;
				EMPCOL [ Y ] := 'FALSE' ;
				EMPUP [ X-Y ] := 'FALSE' ;
				EMPDO [ X+Y ] := 'FALSE' ;
				'IF' X = N 'THEN'
					'GOTO' GOTONE
				'ELSE'
					SET ( X + 1 ) ;
				EMPDO [ X+Y ] := 'TRUE' ;
				EMPUP [ X-Y ] := 'TRUE' ;
				EMPCOL [ Y ] := 'TRUE' ;
				COLUMN [ Y ] := 0
			'END'
		'END'
	'END';

	'COMMENT'
		MAIN PROGRAM START
	;

	OUTSTRING (1, `LOOKING ONTO A ');
	OUTINTEGER (1, N);
	OUTSTRING (1, ` X ');
	OUTINTEGER (1, N);
	OUTSTRING (1, ` CHESSBOARD...\N');

	'FOR' I := 1 'STEP' 1 'UNTIL' N 'DO'
	'BEGIN'
		 COLUMN [ I ] := 0 ;
		 EMPCOL [ I ] := 'TRUE'
	'END';

	'FOR' I := -N+1 'STEP' 1 'UNTIL' N-1 'DO'
		 EMPUP [ I ] := 'TRUE' ;

	'FOR'  I := 2 'STEP' 1 'UNTIL' 2*N 'DO'
		 EMPDO [ I ] := 'TRUE' ;

	SET ( 1 ) ;

	OUTSTRING (1, `NO SOLUTION.\N');
	'GOTO' CONTN;

GOTONE:
	PRINT;

CONTN:
	'IF' N < MAXN 'THEN' 'BEGIN'
		N := N + 1;
		'GOTO' TRY NEXT N
	'END';

	OUTSTRING (1, `DONE.\N')

	'END'
'END'