What’s the difference between these four Add methods (matrix operator overloading) ?Do they all return Matrix?

1.impl<'a, T: ops::Add<Output = T> + Copy> ops::Add for &'a Matrix

type Output = Matrix;

- impl<'a, T: ops::Add<Output = T> + Copy> ops::Add<Matrix> for &'a Matrix

type Output = Matrix;

3.impl<T: ops::Add<Output = T> + Copy> ops::Add for Matrix

type Output = Self;

4.impl<'a, T: ops::Add<Output = T> + Copy> ops::Add<&'a Self> for Matrix

type Output = Self;