use strict;
use warnings;

my $p1 = {'a' => {'x' => 10, 'y' => 20}};
for (sort keys %$p1) {
    print "$_\n";
    my $p2 = $p1->{$_};
    for (sort keys %$p2) {
        print "  $_ => $p2->{$_}\n";
    }
}
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