'begin'
	'comment'
		some if stmts ...
	;

	'procedure' out (x); outinteger (1, x);

	vprint ("expect:\n 1  2  4  5  7  9  10  11  13  15  17\nsee:");
	'if' 'true' 'then' out (1);
	out (2);
	'if' 'false' 'then' out (3);
	out (4);
	'if' 'true' 'then' out (5) 'else' out (6);
	out (7);
	'if' 'false' 'then' out (8) 'else' out (9);
	out (10);
	'if' 'true' 'then' 'begin'
		'if' 'true' 'then' out (11) 'else' out (12)
	'end';
	out (13);
	'if' 'false' 'then'
		out (14)
	'else'
		'if' 'true' 'then' out (15) 'else' out (16);
	out (17);
	vprint ("\ndone.\n");
'end'