s = 0
unseen = 1
seen(v) = bit test(s, v)
see(v) = s = bit or(s, 2^v); while (seen(unseen), unseen++)

other(p) = {
	see(p);
	for (v=unseen, oo,
		if (!seen(v) && hammingweight(bitand(p,v))%2==0,
			return (v);
		);
	);
}

for (n=1, 10 000, print (n " " v=if (n==1, 1, other(v))))

quit