allocate mem(2^30)

\\ |   |   |
\\ +---+---+
\\ |   |   |
\\ +-+-*-*-+   y=3
\\   |   |
\\ --+---*--   y=2
\\   |   |
\\ +-+-*-*-+   y=1
\\ |   |   |
\\ +---O---+   y=0
\\ |   |   |
\\ +-+-+-+-+
neighbours(z) = {
	my (x=real(z)%2, y=imag(z)%4);
	if (y==0 && x==0, return ([z-2, z+2, z-I, z+I]),
	    y==1 && x==0, return ([z-1, z+1, z-I     ]),
	    y==1 && x==1, return ([z-1, z+1,      z+I]),
	    y==2 && x==1, return ([z-2, z+2, z-I, z+I]),
		y==3 && x==0, return ([z-1, z+1,      z+I]),
		y==3 && x==1, return ([z-1, z+1, z-I     ]),
		              print("*** " z); quit);
}

all = Set()
cur = Set([I])	\\ trivalent node

{
	for (n=0, 1 000,
		print (n " " #cur);
		all = set union(all, cur);
		cur = set minus(Set(concat(apply(neighbours, cur))), all);
	);
}

quit