First of all, the reason I am asking the question here is because
as far as I can tell, Maple refuses to provide documentation for their
product (yes, I know, I should have bought mathematica; THEY post 
documentation on their website).

Suppose I type in something like
 a:= array(1..3**8);

How can I write a function first_index so that first_index(a) will return
1 (i.e., the lower bound for a valid index to a)?

Simillarly, how can I write a function last_index so that last_index(a) will
return 6561 (i.e., the upper bound for a valid index to a)?