Recursing downward is one of the stage during code example

Example: Recursion

/**
 * Return all subsequences of word (as defined above) separated by commas,
 * with partialSubsequence prepended to each one.
 */
private static String subsequencesAfter(String partialSubsequence, String word) {
    if (word.isEmpty()) {
        // base case
        return partialSubsequence;
    } else {
        // recursive step
        return subsequencesAfter(partialSubsequence, word.substring(1))
             + ","
             + subsequencesAfter(partialSubsequence + word.charAt(0), word.substring(1));
    }
}