createDirectedGraph("ab", "bc", "cd", "da");

  /**
   * Same as {@link #CYCLE_GRAPH}, but with an extra a->c edge.
   *
   * <pre>{@code
   * |--------------|
   * v              |
   * a -> b -> c -> d
   * |         ^
   * |---------|
   * }</pre>
   */
  private static final SuccessorsFunction<Character> TWO_CYCLES_GRAPH =
      createDirectedGraph("ab", "ac", "bc", "cd", "da");

  /**

      createDirectedGraph("ab", "bc", "cd", "da");

  /**
   * Same as {@link #CYCLE_GRAPH}, but with an extra a->c edge.
   *
   * <pre>{@code
   * |--------------|
   * v              |
   * a -> b -> c -> d
   * |         ^
   * |---------|
   * }</pre>
   */
  private static final SuccessorsFunction<Character> TWO_CYCLES_GRAPH =
      createDirectedGraph("ab", "ac", "bc", "cd", "da");

  /**

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