Chain store

Awarded at past IPP, this puzzle comes from the genius mind of the designer Goh Pit Khiam and was made by the very talentuous Tom Lensch.

Tom is used to crafting puzzles made by Pit Khiam and his puzzles are usually very good and have a little something that makes them very special. Just take the example of this puzzle: packing puzzles are common, not original. But packing puzzles using a chain of 5 links...well I have never seen it before! Have you?

Despite the fragile look of the chain, I can say that it's strong enough (unless you use useless brute force!) to be handled and manipulated without fear that the chain breaks. You have to believe the ability of Tom, he knows what he crafts!!!

I have played with the puzzle for some time before finding the solution and I would say it's pretty challenging, but not overly difficult compared to many other packing puzzles.
It's easy to put some part of the chain inside the box, but it's way more challenging to put all the chain, and remember that you have to pack the chain so that the top is flat...! :-)

Next attempt may be the right one....maybe...

My method was to try packing the chain outside of the box and see how it can fit or not inside. And I do think it's better to play like that, because you may not be able to arrange the links of the chain when the chain is inside the box. No force needed, just clever moves to try to make the chain "as small as possible" without too many holes or useless gaps.

There is only one solution and I really wonder how you can find that there is only one solution and how to write a program that gives you the precise solution..Nevermind, it's another kind of puzzle I assume...