def matmul(mat, rhs):
    """
    Computes a matrix multiplication between a matrix (mat) and a right hand side (rhs).
    If mat is a tensor, then this is the same as torch.matmul.
    This function can work on lazy variables though

    Args:
        - mat (matrix nxn) - left hand size matrix
        - rhs (matrix nxk) - rhs matrix or vector

    Returns:
        - matrix nxk
    """
    return mat.matmul(rhs)