// http://paulbourke.net/geometry/circlesphere/ Intersection of two circles
function vector intersectionTwoCiclesLeft(vector p0, p1; float radius0, radius1) {
    float d = distance(p0, p1);
    float a = (radius0 * radius0 - radius1 * radius1 + d * d) / (2*d);
    float h = sqrt(radius0 * radius0 - a * a);

    vector p2 = p0 + a * (p1 - p0) / d;

    // xz
    return set(
        p2.x - h*(p1.z - p0.z)/d,
        p2.y,
        p2.z + h*(p1.x - p0.x)/d
    );
}