p = vector(5 000, n, [])	\\ parents
u = 2

{
	m = 0;
	rr = [];	\\ previous row
	for (n=1, #p,
		r = binomial(n);

		for (k=2, #r-1,
			c = r[k];
			if (c > #p,
					break,
					p[c] = setunion(p[c], Set([rr[k-1], rr[k]]));
			);
		);

		rr = r;

		apply (v -> print (m++ " " v), p[n]);
	);
}

quit