* serialization of funnels. When possible, it is recommended that funnels be implemented as a
 * single-element enum to maintain serialization guarantees. See Effective Java (2nd Edition), Item
 * 3: "Enforce the singleton property with a private constructor or an enum type". For example:
 *
 * {@snippet :
 * public enum PersonFunnel implements Funnel<Person> {
 *   INSTANCE;
 *   public void funnel(Person person, PrimitiveSink into) {

    }

    List<String> visitAll() {
        return visitAll(vertices.values(), new HashMap<>(), new ArrayList<>());
    }

    List<String> findCycle(Vertex vertex) {
        return visitCycle(Collections.singleton(vertex), new HashMap<>(), new LinkedList<>());
    }

    private static List<String> visitAll(
            Collection<Vertex> children, Map<Vertex, DfsState> stateMap, List<String> list) {

 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.repository.internal;

import javax.inject.Inject;
import javax.inject.Named;
import javax.inject.Singleton;

import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Properties;

import org.apache.maven.model.Model;

 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.exception;

import javax.inject.Named;
import javax.inject.Singleton;

import java.io.IOException;
import java.net.ConnectException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.IdentityHashMap;

    return NaturalOrdering.INSTANCE.min(iterator);
  }

  @Override
  public <E extends Comparable<?>> E max(Iterable<E> iterable) {
    return NaturalOrdering.INSTANCE.min(iterable);
  }

  // preserving singleton-ness gives equals()/hashCode() for free
  private Object readResolve() {
    return INSTANCE;
  }

  @Override
  public String toString() {
    return "Ordering.natural().reverse()";
  }

    synchronized void addEdge(String from, String to) throws CycleDetectedException {
        if (graph.computeIfAbsent(from, l -> new HashSet<>()).add(to)) {
            List<String> cycle = visitCycle(graph, Collections.singleton(to), new HashMap<>(), new LinkedList<>());
            if (cycle != null) {
                // remove edge which introduced cycle
                throw new CycleDetectedException(

  }

  public void testMapDifferenceEmptySingleton() {
    MapDifference<Integer, Integer> diff = Maps.difference(EMPTY, SINGLETON);
    assertFalse(diff.areEqual());
    assertEquals(EMPTY, diff.entriesOnlyOnLeft());
    assertEquals(SINGLETON, diff.entriesOnlyOnRight());
    assertEquals(EMPTY, diff.entriesInCommon());
    assertEquals(EMPTY, diff.entriesDiffering());

import org.apache.maven.api.Lifecycle;
import org.apache.maven.api.cli.mvnup.UpgradeOptions;
import org.apache.maven.api.di.Named;
import org.apache.maven.api.di.Priority;
import org.apache.maven.api.di.Singleton;
import org.apache.maven.cling.invoker.mvnup.UpgradeContext;

import static eu.maveniverse.domtrip.maven.MavenPomElements.Elements.BUILD;
import static eu.maveniverse.domtrip.maven.MavenPomElements.Elements.EXECUTIONS;

  @SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
  public <S extends Comparable<?>> Ordering<S> reverse() {
    return (Ordering<S>) ReverseNaturalOrdering.INSTANCE;
  }

  // preserving singleton-ness gives equals()/hashCode() for free
  private Object readResolve() {
    return INSTANCE;
  }

  @Override
  public String toString() {
    return "Ordering.natural()";
  }

 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.lifecycle.internal;

import javax.inject.Inject;
import javax.inject.Named;
import javax.inject.Singleton;
import javax.xml.stream.XMLStreamException;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;