Update textbook

_sources/chapters/intro/3110.md

@@ -10,7 +10,7 @@ same name, and it used Scheme, a functional programming language. Tim Teitelbaum
 taught a version of the course at Cornell in Fall 1988, following the book
 rather closely and using Scheme.
 
-[sicp]: https://mitpress.mit.edu/sites/default/files/sicp/index.html
+[sicp]: https://web.mit.edu/6.001/6.037/sicp.pdf
 
 **CS 212.** Dan Huttenlocher had been a TA for 6.001 at MIT; he later became
 faculty at Cornell. In Fall 1989, he inaugurated CS 212 Modes of Algorithm

chapters/intro/3110.html

@@ -524,7 +524,7 @@ <h1><span class="section-number">1.4. </span>A Brief History of CS 3110<a class=
 has existed for over two decades and has always taught functional programming,
 but it has not always used OCaml.</p>
 <p>Once upon a time, there was a course at MIT known as 6.001 <em>Structure and
-Interpretation of Computer Programs</em> (SICP). It had a <a class="reference external" href="https://mitpress.mit.edu/sites/default/files/sicp/index.html">textbook</a> by the
+Interpretation of Computer Programs</em> (SICP). It had a <a class="reference external" href="https://web.mit.edu/6.001/6.037/sicp.pdf">textbook</a> by the
 same name, and it used Scheme, a functional programming language. Tim Teitelbaum
 taught a version of the course at Cornell in Fall 1988, following the book
 rather closely and using Scheme.</p>