code: func (set *Set) All(items ...interface{}) bool {
  	set.lock.RLock()
  	defer set.lock.RUnlock()
  
  	for _, item := range items {
  		if _, ok := set.items[item]; !ok {
  			return false
  		}
  	}
  
  	return true
  }
docs: // All returns a bool indicating if all of the supplied items exist in the set.