Key and Lock Puzzles in procedural gameplay.

While researching through the references of the Case Study on Charbitat I found this paper. It is great. it describes how key and lock puzzles can be played in a procedural game world.

" Abstract:
This project is an attempt to model and simulate key and lock puzzles in the style of Shigeru Miyamoto games, specifically the Zelda and Metroid series. Much of the gameplay in these titles is oriented around encountering obstacles, and then locating an item that allows the player to circumvent the obstacle. The project is built on top of Charbitat, another project built on Unreal Tournament 2004, which produces procedurally generated space in response to the player's actions. " (source)