> For the complete documentation index, see [llms.txt](https://light-in-the-dark-1.gitbook.io/litd/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://light-in-the-dark-1.gitbook.io/litd/core-in-game-buildings/library.md).

# Library

Before upgrading buildings to sequential levels, players must first learn the required knowledge of that upgrade in the library. Library unlocks will require players to spend $LIGHT tokens but will be worth the investment in the long run. Once you have obtained the necessary knowledge, you will then be able to spend resources to actually construct the upgrade. First you must learn the upgrade in the library, then you may build it using in-game resources. 

<figure><img src="/files/lh2AdK7oq4CUunp8yiFo" alt=""><figcaption><p>The Library</p></figcaption></figure>

**Resource buildings are not subject to learning requirements in the library.**&#x20;

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