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constructing maps between modules

Let's start with a free module.
i1 : R = ZZ/5[x,y,z];
i2 : F = R^3

      3
o2 = R

o2 : R-module, free
A list of indices can be used to produce homomorphisms corresponding to the corresponding basis vectors.
i3 : F_{0,1,2}

o3 = | 1 0 0 |
     | 0 1 0 |
     | 0 0 1 |

             3      3
o3 : Matrix R  <-- R
i4 : F_{0,1}

o4 = | 1 0 |
     | 0 1 |
     | 0 0 |

             3      2
o4 : Matrix R  <-- R
i5 : F_{1,2}

o5 = | 0 0 |
     | 1 0 |
     | 0 1 |

             3      2
o5 : Matrix R  <-- R
Matrices are viewed as linear transformations.
i6 : f = matrix{{x,y,z}}

o6 = | x y z |

             1      3
o6 : Matrix R  <-- R