[a, b; c, d]·[1, 0; 1, 1] = [1, 0; 1, 1]·[a, b; c, d]
b = 0 und a = d
[a, 0; c, a]
[a, b; c, d]·[e, f; g, h] = [e, f; g, h]·[a, b; c, d]
[a·e + b·g, a·f + b·h; c·e + d·g, c·f + d·h] = [a·e + c·f, b·e + d·f; a·g + c·h, b·g + d·h]
b = c = 0
a = d
[a, 0; 0, a]