Just out of curiosity, I know there's still a lot up in the air (err?), but won't this be a syntax error?

    @seen{@data} ^= 1;
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You have an @ to designate "seen" as an array (Perl6 terminology, folks!, I know that's not correct for Perl5), but you're using the curlies for a hash. I am assuming that what you meant to do was use a hash slice of elements in @data and set all elements to 1 (true). If so, I believe that would be:

    %seen{@data} ^= 1;
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For those not familiar with Perl 6 idioms, that would be the equivalent of the following in Perl 5:

    @seen{@data} = (1) x @data;

    # or

    foreach (@data)
    {
        $seen{ $_ } = 1;
    }
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Cheers,
Ovid

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