link matrix

procedure main ()
  m1 := [[1,2,3], [4,5,6]]
  m2 := [[1,2],[3,4],[5,6]]
  m3 := mult_matrix (m1, m2)
  write ("Multiply:")
  write_matrix ("", m1) # first argument is filename, or "" for stdout
  write ("by:")
  write_matrix ("", m2)
  write ("Result: ")
  write_matrix ("", m3)
end