+<li><a href="http://freico.in/docs/freimarkets.pdf">Freimarkets: a bitcoin extension to support user issued assets, p2p lending, options and more.</a>
+<li><a href="https://bitcoin.org/bitcoin.pdf">Bitcoin: A Peer-to-Peer Electronic Cash System</a></li>
+</ul>
+
+<a href="http://sagemath.org/">Sage</a> notebooks:
+<ul>
+<li><a href="secp256k1.ecdsa.sage">ECDSA with secp256k1</a>