I don't know what exactly author wants,
maybe this?
to detect whether a number belongs to a pool of defined similarity

@a = qw/5 7 2 5 1 3/;
undef @{$h{a}}{5, 4, 3};
undef @{$h{b}}{7, 9, 6};
undef @{$h{c}}{0, 2, 1};

for $x (@a){
        exists $h{$_}{$x} and print "$x pool $_\n" for keys %h;
}
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