fix: correct broken PARRY paper DOI in course materials

The Colby et al. (1971) PARRY paper link had an incorrect DOI format.
- Old: doi.org/10.1016/S0004-3702(71)80014-6 (broken)
- New: doi.org/10.1016/0004-3702(71)90002-6 (verified working)

Updated in both slides/README.md and admin/syllabus.md.

Link audit verified 36 academic/course links total - all others valid.

Author: jeremymanning

admin/syllabus.md

@@ -155,7 +155,7 @@ We strive to create an inclusive learning environment where all students feel su
 | Mon Jan 5 | Lecture 1 | Course Introduction, Is ChatGPT Conscious? | [HTML](../slides/week1/lecture1.html), [PDF](../slides/week1/lecture1.pdf) | [Fedorenko et al. (2024)](https://www.nature.com/articles/s41586-024-07522-w), [Lupyan et al. (2020)](https://doi.org/10.1016/j.tics.2020.08.005) |
 | Wed Jan 7 | Lecture 2 | Pattern Matching & ELIZA | [HTML](../slides/week1/lecture2.html), [PDF](../slides/week1/lecture2.pdf) | [Weizenbaum (1966)](https://web.stanford.edu/class/cs124/p36-weizenabaum.pdf) |
 | Thu Jan 8 | Lecture 3 | ELIZA Implementation | [HTML](../slides/week1/lecture3.html), [PDF](../slides/week1/lecture3.pdf) | |
-| Fri Jan 9 | Lecture 4 | Rules-Based Chatbots | [HTML](../slides/week1/lecture4.html), [PDF](../slides/week1/lecture4.pdf) | [Colby et al. (1971)](https://doi.org/10.1016/S0004-3702%2871%2980014-6), **[Assignment 1](../assignments/assignment-1/) Released** |
+| Fri Jan 9 | Lecture 4 | Rules-Based Chatbots | [HTML](../slides/week1/lecture4.html), [PDF](../slides/week1/lecture4.pdf) | [Colby et al. (1971)](https://doi.org/10.1016/0004-3702%2871%2990002-6), **[Assignment 1](../assignments/assignment-1/) Released** |
 
 ### Week 2: Computational Linguistics (January 12--16)
 

slides/README.md

@@ -58,7 +58,7 @@ Explore concepts hands-on with our interactive web demos! Each demo runs directl
 - A.L.I.C.E. and AIML: pattern-based conversation design
 - The evolution from ELIZA to modern rules-based systems
 - **Assignment 1 Released:** [Building the ELIZA Chatbot](https://contextlab.github.io/llm-course/assignments/assignment-1/) (Due: Jan 19, 11:59 PM EST)
-- Reading: [Colby et al. (1971)](https://doi.org/10.1016/S0004-3702(71)80014-6) - Artificial Paranoia (PARRY)
+- Reading: [Colby et al. (1971)](https://doi.org/10.1016/0004-3702(71)90002-6) - Artificial Paranoia (PARRY)
 - Reference: [ALICE/AIML Foundation](https://www.alicebot.org/)
 - 🎮 **Try it:** [ELIZA Demo](https://contextlab.github.io/llm-course/demos/eliza/) | [Chatbot Evolution](https://contextlab.github.io/llm-course/demos/chatbot-evolution/)
 - 📊 [Slides PDF](https://contextlab.github.io/llm-course/slides/week1/lecture4.pdf) | 🌐 [Slides HTML](https://contextlab.github.io/llm-course/slides/week1/lecture4.html)