// "Collapse loop with stream 'findFirst()'" "true-preview"

import java.util.Collection;
import java.util.List;

public class Main {
  public static String find(List<List<String>> list) {
      return list.stream().flatMap(Collection::stream).filter(string -> string.startsWith("ABC")).findFirst().filter(string -> string.substring(3).equals("xyz")).map(String::trim).orElse(null);
  }
}