Nested for-statements in Maxima

Hello!

I'm new to Maxima, and i have a problem. I suppose the solution is simple,
but i didn't find any
in the Maxima-related docs.

I need to do something like this (in Fortran):

DO i=1,n
  DO J=1,k
      ! some assigments to the array elements here
      a(i,j) = some_function_of_ij
      b(i,j) = another_function_of_ij

  ENDDO
ENDDO

I've tried the following solution:

FOR i:1 THRU n DO
   FOR j:1 THRU k DO
      a[i,j]:some_function_of_ij,
      b[i,j]:another__function_of_ij$

but it doesn't work. Only the first assigment (a[i,j]:...) is perfomed in a
right way.
I think i use nested for-statements in a wrong way.

If i make only one assigment in the loop body, i.e.

FOR i:1 THRU n DO
   FOR j:1 THRU k DO
      a[i,j]:some_function_of_ij$

everything is ok.

So, what's wrong and how to do it correctly?
Just point me to the related docs or to the simple example.

Thanks a lot.

Best regards,
Gene