function solve(bones, target) {
  let effector = bones[bones.length - 1];

  for (let j = 2; j < bones.length; j++) {
    for (let i = bones.length - 2; i >= bones.length - j; i--) {
      let bone = bones[i];
      let bonePos = worldPos(bone);

      let v1 = worldPos(effector).sub(bonePos);
      let v2 = worldPos(target).sub(bonePos);
      let angle = v1.angleTo(v2);

      let axis = new THREE.Vector3();
      axis.crossVectors(v1, v2).normalize();
      bone.rotateOnAxis(axis, angle);
    }
  }
}