my %hash;             # the % sigil denotes a hash
$hash{'element'} = 1; # the $ sigil denotes a scalar value (the 'eleme
+nt' element of %hash)
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Similarly, the @ sigil in @$A{keys %b} denotes list context. I believe it interpolates as (verified):

@$A{(c,d,f)} = (9, 16, 36);

Which is essentially the same thing as:

$A{c} = 9;
$A{d} = 16;
$A{f} = 36;
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Given that $A = \%a, you could skip the reference:

$a{c} = 9;
$a{d} = 16;
$a{f} = 36;
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