Assignment compatibility with transfer procedures

In the statements

   pack(a,i,z)

and

   unpack(z,a,i)

the value of i shall be assignment compatible with the index type of the array variable a.

For example given:

   var a : array[1..100] of real;
       z : packed array[1..100] of real;
       i : integer;

and

   pack(a,i,z) or unpack(z,a,i)

then i shall be assignment compatible with

   1..100 (the index-type of a).