sub sum_of_squared_pairs {
    reduce { $a + $b } map { $_ * $_ } grep { $_ % 2 == 0 } @_
  }

  sub schwartzian_transform {
    map  { $_->[0] }
    sort { $a->[1] <=> $b->[1] } # use numeric comparison
    map  { [$_, length $_] }     # calculate the length of the string
         @_
  }