code: public static <T> Collection<T> intersect(Collection<T> left, Collection<T> right) {
          return intersect(left, right, new NumberAwareComparator<>());
      }
docs: Create a Collection composed of the intersection of both collections.  Any
  elements that exist in both collections are added to the resultant collection.
  For collections of custom objects; the objects should implement java.lang.Comparable
  <pre class="groovyTestCase">assert [4,5] == [1,2,3,4,5].intersect([4,5,6,7,8])</pre>
  By default, Groovy uses a {@link NumberAwareComparator} when determining if an
  element exists in both collections.
  
  @param left  a Collection
  @param right a Collection
  @return a Collection as an intersection of both collections
  @see #intersect(Collection, Collection, Comparator)
  @since 1.5.6