a: matrix([1, 2],
          [3, 4],
          [5, 6],
          [7, 8])$

b: matrix([1, 2, 3],
          [4, 5, 6])$

a . b;
/* matrix([ 9, 12, 15],
          [19, 26, 33],
          [29, 40, 51],
          [39, 54, 69]) */