Neutrales Element der Multiplikation

http://maxima-online.org/?inc=r1344373592
(%i1) A:matrix([0,2,0],[0,0,4],[5,3,0]);
                                  [ 0  2  0 ]
                                  [         ]
(%o1)                             [ 0  0  4 ]
                                  [         ]
                                  [ 5  3  0 ]
(%i2) E1:matrix([1,0,0],[0,1,0],[0,0,1]);
                                  [ 1  0  0 ]
                                  [         ]
(%o2)                             [ 0  1  0 ]
                                  [         ]
                                  [ 0  0  1 ]
(%i3) A.E1;
                                  [ 0  2  0 ]
                                  [         ]
(%o3)                             [ 0  0  4 ]
                                  [         ]
                                  [ 5  3  0 ]
(%i4) E1.A;
                                  [ 0  2  0 ]
                                  [         ]
(%o4)                             [ 0  0  4 ]
                                  [         ]
                                  [ 5  3  0 ]
(%i5) B:matrix([2,3],[0,2]);
                                   [ 2  3 ]
(%o5)                              [      ]
                                   [ 0  2 ]
(%i6) E2:matrix([1,0],[0,1]);
                                   [ 1  0 ]
(%o6)                              [      ]
                                   [ 0  1 ]
(%i7) B.E2;
                                   [ 2  3 ]
(%o7)                              [      ]
                                   [ 0  2 ]
(%i8) E2.B;
                                   [ 2  3 ]
(%o8)                              [      ]
                                   [ 0  2 ]