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use strict;
use warnings;
...
    }
    return @rv;
}

({ 42 => [5, 11] }, { 7 => [6, 9] }, { 2 => [1, 2, 7] })

use strict;
use warnings;
...
    delete @buckets{ grep { @{$buckets{$_}} < 2 } keys %buckets };
    return %buckets;
}

{ 2 => [1, 2, 7], 7 => [6, 9], 42 => [5, 11] }