The reason it's saying "Not an ARRAY reference" is because it's not an array reference. Add the missing sigils, and the error disappears: 
...
@a_a = (\@a_4, \@a_3);
@a_b = (\@a_2, \@a_a);
...

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In reply to Re: Multidimensional Array by everybody
in thread Multidimensional Array by burgerw

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