$A[$_]		-- the element of @A at the current index
$First{ $A[$_] }	-- the previous line is a key in %First
@{ }			-- and the associated value is an anonymous array

##</code><code>##

Elements of @A:
0	zero
1	one
2	two

Elements of %First:
zero	[ 0 ]
one	[ 1 ]
two	[ 2 ]