code: public static <T> Set<List<T>> subsequences(List<T> self) {
          return GroovyCollections.subsequences(self);
      }
docs: Finds all non-null subsequences of a list.
  <p>
  Example usage:
  <pre class="groovyTestCase">def result = [1, 2, 3].subsequences()
  assert result == [[1, 2, 3], [1, 3], [2, 3], [1, 2], [1], [2], [3]] as Set</pre>
  
  @param self the List of items
  @return the subsequences from the list
  @since 1.7.0