sub fold_sort {
    my ( $x, $y ) = ( $a, $b );
    for ( $x, $y ) {
        tr/A-Z/a-z/;
        tr/ÀÁÂÃÄÅàáâãäå/a/;
        tr/ÈÉÊËèéêë/e/;
        tr/ÌÍÎÏìíîï/i/;
        tr/ÒÓÔÕÖØòóôõöø/o/;
        tr/ÙÚÛÜùúûü/u/;
        tr/ÇçÑñÝýÿ/ccnnyyy/;
        s/ß/ss/g;
    }
    $x cmp $y;
}