F matrix_mul(m1, m2)
   assert(m1[0].len == m2.len)
   V r = [[0.0] * m2[0].len] * m1.len
   L(j) 0 .< m1.len
      L(i) 0 .< m2[0].len
         V s = 0.0
         L(k) 0 .< m2.len
            s += m1[j][k] * m2[k][i]
         r[j][i] = s
   R r

F to_str(m)
   V result = ‘([’
   L(r) m
      I result.len > 2
         result ‘’= "]\n ["
      L(val) r
         result ‘’= ‘#5.2’.format(val)
   R result‘])’

V a = [[1.0,  1.0,  1.0,   1.0],
       [2.0,  4.0,  8.0,  16.0],
       [3.0,  9.0, 27.0,  81.0],
       [4.0, 16.0, 64.0, 256.0]]

V b = [[    4.0, -3.0  ,  4/3.0,   -1/4.0],
       [-13/3.0, 19/4.0, -7/3.0,  11/24.0],
       [  3/2.0, -2.0  ,  7/6.0,   -1/4.0],
       [ -1/6.0,  1/4.0, -1/6.0,   1/24.0]]

print(to_str(a))
print(to_str(b))
print(to_str(matrix_mul(a, b)))
print(to_str(matrix_mul(b, a)))