*[Object-Oriented Programming in the BETA Programming Language](https://beta.cs.au.dk/Books/) - Ole Lehrmann Madsen, Birger Møller-Pedersen, Kristen Nygaard
*[MIA 99-42: The Fragment System: Further Specification](https://beta.cs.au.dk/Manuals/latest/beta/fragment.html) - Mjølner Informatics
*[Object-Oriented Programming in the BETA Programming Language](https://beta.cs.au.dk/Books/) - Ole Lehrmann Madsen, Birger Møller-Pedersen, Kristen Nygaard