sink find20
  def a: $;
  1 -> #
  when <..$a::length> do def i: $;
    '$#10;' -> !OUT::write
    1 -> \(
      when <$a($i)::length~..> do $i + 1 !
      otherwise def j: $;
        def val: $a($i;$j);
        ' $val;' -> !OUT::write
        $val -> \(<~=20> $j + 1 ! \) -> #
    \) -> #
end find20

[1..10 -> [1..10 -> 20 -> SYS::randomInt -> $ + 1]] -> !find20