tr(v)=if (v>=0, 1+2*v, -2*v)
s = []
black(z)=my (x=tr(real(z)),y=tr(imag(z))); if (x>#s, 0, bittest(s[x],y))
flip(z)=my (x=tr(real(z)),y=tr(imag(z))); if (x>#s, s=concat(s,vector(x-#s))); s[x]=bitxor(s[x],2^y)

ants = [ -1, +1 ]
dirs = [ +I, +I ]
nb = 0

{
	for (n=0, 20 000,
		print (n " " nb);
		for (i=1, #ants,
			if (black(ants[i]),
				dirs[i] /= I,
				dirs[i] *= I
			);
		);
		apply (z -> if (black(z), nb--, nb++); flip(z), Set(ants));
		ants += dirs;
	);
}

quit