PDF Links in README give 404

The links describing sigmoidal programming problems and the branch-and-bound method used give a 404 error for me as of today. I was able to find the documents using the Wayback machine but it would be great if the links could be updated (assuming they are presently hosted somewhere else).

Start in the repository README and inspect the links describing sigmoidal programming problems and the branch-and-bound method. Find current hosted versions of the referenced documents, then update the links and verify that both no longer return 404 errors.

Written by the indexing model from the issue text.