Hi Joaquín,

  multi_index_conainer<     T,     ordered_non_unique<       composite_key<         T,         member,         member       >     >,     ordered_non_unique<...>   > my_container;

Now, if you do an equal_range on a category elements will indeed be sorted by the second member.

Right. Here is a better formulated question then: Let's say c1 is an object of type category_t. When I apply equal_range for c1, will I get my desired range in log(n) time (where n == my_container.size())? Or, will I get it in O(1) for the elements are already stored in a category-by-category manner? TIA, --Hossein