big = 1 000 000
s = 0
S = []
unseen = 0
seen(v) = if (v < big, bittest(s, v), setsearch(S, v))
see(v) = if (v < big, s = bitor(s, 2^v), S = setunion(S, [v])); while (seen(unseen), unseen++)

\\ least k unseen / v AND k = 0
cc = [0]
avoid(v) = {
	if (!seen(0),
		return (0);
	);
	my (b, c, nb=1);
	for (e=0, oo,
		if (!bittest(v,e),
			if (nb==#cc,
				cc=concat(cc, vector(#cc));
			);
			b=2^e;
			for (k=1, nb,
				c = cc[nb+k] = cc[k]+b;
				if (!seen(c),
					return (c);
				);
			);
			nb*=2;
		);
	);
}

n = 0
a = [0]

b = vector(10 000)
u = 1

emit(v) = {
	n++;

	if (v && v <= #b,
		b[v] = n-1;
		while (b[u],
			print (u " " b[u]);
			if (u++ > #b,
				quit;
			);
		);
	);

	see(v);

	if (n > #a,
		a = concat(a, vector(#a));
	);
	a[n] = v;
}

{
	print ("0 0");

	emit(0);
	for (n = 1, oo,
		emit(v = avoid(a[n]));
		emit(avoid(v + a[n]));
	);
}

quit