sub mergesort
  {
  @_ < 2 and return @_;
  my @low = mergesort( @_[0 .. $#_ / 2] );
  my @high = mergesort( @_[$#_ / 2 + 1 .. $#_] );
  map !@high || @low && $low[0] <= $high[0] ? shift @low : shift @high, 1..@_;
  }