furthermore, in your example the elements from the "alphabet" always only appear once

'a{b,c}d{e,fg{,h,ij}k}l{,m{n,o}}';

I suppose that is not a given, but this might guaranty a unique solution.

OTOH if characters can be repeated I'd bet that multiple solutions are possible.

Please clarify.

update

for instance all these glob expressions are equivalent ( I removed the variations where {,a} and {a,} were swapped)

use v5.12;
use warnings;
use Data::Dump;
use Test::More;

test (
      [ <{a,aa}> ],
      [ <{,a}{a}> ],
      [ <{a}{,a}> ],
      [ <a{,a}> ],
      [ <{,a}a> ],
     );

sub test {
    my @g = @_;
    my (%h1,%h2);
    for my $i (0..$#g) {
        for my $j ($i+1..$#g) {
            is_deeply(
                      [sort @{$g[$i]}],
                      [sort @{$g[$j]}],
                      "$i,$j")
              or ddx $g[$i],$g[$j];
        }
    }
}

done_testing;
[download]