-- -*- M2-comint -*- {* hash: -2101685508 *}

i1 : R = ZZ[a..d];

i2 : M = image matrix {{a,b}}

o2 = image | a b |

                             1
o2 : R-module, submodule of R

i3 : N = image matrix {{c,d}}

o3 = image | c d |

                             1
o3 : R-module, submodule of R

i4 : M ** N

o4 = cokernel {2} | -d 0  -b 0  |
              {2} | c  0  0  -b |
              {2} | 0  -d a  0  |
              {2} | 0  c  0  a  |

                            4
o4 : R-module, quotient of R

i5 : N ** M

o5 = cokernel {2} | -b 0  -d 0  |
              {2} | a  0  0  -d |
              {2} | 0  -b c  0  |
              {2} | 0  a  0  c  |

                            4
o5 : R-module, quotient of R

i6 :