sub natural_cmp ($a is copy, $b is copy) {
   return $a.subst(/(\d+)/, -> $/{ sprintf( "%s%c%s", 0, $0.chars, $0) }, :g).lc
   cmp $b.subst(/(\d+)/, -> $/{ sprintf( "%s%c%s", 0, $0.chars, $0) }, :g).lc;
}