void Horocycle()
{
	const double DIMX = 800;
	const double DIMY = 800;
	const double B    = 32;

	FILE * fp = fopen("c:\\temp\\horocycle.svg","w");

	fprintf(fp,
		"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
		"<svg\n"
		"xmlns:svg=\"http://www.w3.org/2000/svg\"\n"
		"xmlns=\"http://www.w3.org/2000/svg\"\n"
		"version=\"1.0\"\n"
		"width=\"%g\"\n"
		"height=\"%g\"\n"
		"id=\"rocco\">\n"
		,DIMX,DIMY
	);

	circle2 gc; gc.c = point2(DIMX/2,DIMY/2); gc.r = (DIMX-2*B)/2;

	fprintf(fp,"<circle cx=\"%g\" cy=\"%g\" r=\"%g\" style=\"fill:#ffffE0;stroke:#000000;stroke-width:3;stroke-opacity:1\" />\n"
		,gc.c.x,gc.c.y
		,gc.r
	);	

	circle2 hc; hc.r = DIMX/3; hc.c = point2(DIMX/2,B+hc.r);

	fprintf(fp,"<circle cx=\"%g\" cy=\"%g\" r=\"%g\" style=\"fill:none;stroke:#0000A0;stroke-width:3;stroke-opacity:1\" />\n"
		,hc.c.x,hc.c.y
		,hc.r
	);

	const int N = 24;
	int i;
	for(i=0;i<N;++i)
	{
		double a = 2*PI*i/N + PI/N;
		point2 p = hc.point(a);

		fprintf(fp,"<circle cx=\"%g\" cy=\"%g\" r=\"%g\" style=\"fill:#000000;stroke:#000000;stroke-width:3;stroke-opacity:1\" />\n"
			,p.x,p.y
			,4.0
		);

		segment2 s( p, point2(DIMX/2,B) );
		line2 ax; s.axis(ax);
		line2 ba; ba.orig.x = DIMX/2; ba.orig.y = B; ba.dire.x = 1; ba.dire.y = 0;
		point2 pp; line_line_int(ax,ba,pp);
		double ra = dist(pp,p);

		circle2 cc; cc.c = pp; cc.r = ra;
	
		point2 p1,p2; intersection(cc,gc,p1,p2);

		fprintf(fp,"<path d=\"M%g,%g A%g,%g 0 0,1 %g,%g\" style=\"fill:none;stroke:#800000;stroke-width:1.5;stroke-opacity:1\" />\n"
			,p1.x,p1.y
			,cc.r,cc.r
			,p2.x,p2.y
		);
	}

	fprintf(fp,"</svg>\n");
	fclose(fp);
}