#[derive(Clone, Debug)]
pub struct Vec3 {
    pub v: [f64; 3],
}

impl Sub for Vec3 {
    type Output = Vec3;

    fn sub(self, other: Vec3) -> Vec3 {
        Vec3 {
            v: [
                self.v[0] - other.v[0],
                self.v[1] - other.v[1],
                self.v[2] - other.v[2],
            ],
        }
    }
}

let x = Vec3 {v: [0., 0., 0.]};
    let y = Vec3 {v: [0., 0., 0.]};
    let a = x - y;
    let b = x - y;