> For the complete documentation index, see [llms.txt](https://clarity-bitcoin.gitbook.io/clarity-bitcoin-library/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://clarity-bitcoin.gitbook.io/clarity-bitcoin-library/introduction.md). # Introduction Through Proof of Transfer the Stacks blockchain has a view on the Bitcoin network. It is limted to block header hashes of each Bitcoin block. This includes even those blocks that do not have a corresponding Stacks block e.g. for flash blocks. The block header hash is sufficient to proof in a Clarity contract that a Bitcoin transaction was actually included in the Bitcoin block. It is just a question about providing enough information to re-build the hash. This also works for transaction with witness data. Currently, a stateless contract is deployed on mainnet that helps to make use of this feature for transactions with and without witness data, but limited to transactions with a smaller number of inputs and outputs: The next sections describe the details of the library and its application.