seen   = []
unseen = []
index  = [-1]

other(n,p) = {
	if (n==1,
		return (1);
	);
	if (#seen < p,
		seen   = concat(seen,   0);
		unseen = concat(unseen, 1);
		index  = concat(index, -1);
	);

	for (v=unseen[p], oo,
		if (!bit test(seen[p], v)
			&& (index[v]==-1 || index[v]%2!=n%2),
			seen[p] += 2^v;
			while (bit test(seen[p], unseen[p]),
				unseen[p]++;
			);
			index[v] = n;
			return (v);
		);
	);
}

for (n=1, 10 000, a = other(n, a); print (n " "a))

quit