I started by cloning the AIMA-JAVA repo and left the default branch as "AIMA3e".
I then imported the repo into Eclipse following the instructions shown at https://github.com/aimacode/aima-java/wiki/AIMA3e-Using-Eclipse-IDE, but rather than using a zip, I imported from the root directory of the repo.
Then, I opened aima-core/src/main/java/aima/core/agent/impl/aprog/TableDrivenAgentProgram.java in Eclipse and viewed the code. I then found AgentProgram.java higher in the directory tree and also opened it in the editor.
Now I wanted to view the declaration of Function<P, Optional<A>> so I right clicked on it inside the AgentProgram.java file but, to my surprise, I received an error dialog stating aima-java does not exist. So I went back to the TableDrivenAgentProgram.java file and right clicked on AgentProgram<P, A> and selected Open Declaration in the context menu. However, I received the same error again: aima-java does not exist. See image below.

What do I need to do in Eclipse such that it is able to find declarations of classes, interfaces, etc. within the aima-java codebase?