[Axiom-mail] Setting elements in a matrix

[Fabio S.]

I am sorry, but I can't understand why I am not able to change the 
elements of a square matrix. I tried the following

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

(1) -> m : SquareMatrix(2,INT) := [[1,2],[3,4]]

        +1  2+
   (1)  |    |
        +3  4+
                                                   Type: SquareMatrix(2,Integer)
(2) -> m(1,1):=0

   The form on the left hand side of an assignment must be a single
      variable, a Tuple of variables or a reference to an entry in an
      object supporting the setelt operation.
(2) -> setelt(m,1,1,0)
   There are 2 exposed and 0 unexposed library operations named setelt
      having 4 argument(s) but none was determined to be applicable. Use
      HyperDoc Browse, or issue
                               )display op setelt
      to learn more about the available operations. Perhaps
      package-calling the operation or using coercions on the arguments
      will allow you to apply the operation.

   Cannot find a definition or applicable library operation named setelt
      with argument type(s)
                            SquareMatrix(2,Integer)
                                PositiveInteger
                                PositiveInteger
                               NonNegativeInteger

      Perhaps you should use "@" to indicate the required return type, or
      "$" to specify which version of the function you need.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Where is my mistake?

Thanks

Fabio