I had that same error; Firefox was using a cached version of a Javascript file instead of loading the new one. Typing Ctrl+F5 (Reload & override cache) fixed

I had that same error; Firefox was using a cached version of a Javascript file instead of loading the new one. Typing Ctrl+F5 (Reload & override cache) fixed it. I don't know the command for other browsers. I might try to implement an "another example" feature some time. The program enumerates worlds internally when it is searching for an example/counterexample, so that feature should be doable.